673 Electronic and Computer Controlled Systems Technician Handbook 06-22-09

© 2009 Toyota Motor Sales, U.S.A., Inc.

All rights reserved. This book may not be reproduced or copied, in whole or in part by any means, without the written permission of Toyota Motor Sales, U.S.A., Inc.

Revision Date: June 22, 2009

TOYOTA Technical Training

Electronic & Computer Controlled Systems Course 673 Technician Handbook

Table of Contents 673 Electronic & Computer Controlled Systems

Technical Training i

Objectives Final Student Performances ................................................................ a

Section 1: Diagnostic

Techniques and Tools

Course Menu ....................................................................................... 3 Section 1 Topics .................................................................................. 5 Electronic Control Units ........................................................................ 6 How ECUs Work ................................................................................... 7

Logic Function .................................................................................. 7 Simple ECU Inputs ................................................................................ 8

Voltage ON/OFF (Switch) Input ........................................................ 9 Variable Voltage Input .................................................................... 10 Variable Resistance Input ............................................................... 11 Pulse Pattern Input ......................................................................... 12

Simple ECU Outputs ........................................................................... 13 Transistors as Switches .................................................................. 13

Pulse Width Modulation ...................................................................... 14 Duty Cycle ........................................................................................... 15

Power-Side Control ......................................................................... 16 Self Diagnosis ..................................................................................... 17

Differences in Self-Diagnosis .......................................................... 17 ECU Memory ...................................................................................... 19

Types of ECU Memory ................................................................... 19 Customization ..................................................................................... 20 Initialization ......................................................................................... 21

Why Initialize? ................................................................................. 21

Section 2: Overview of

Multiplex Communication

Section 2 Topics ................................................................................. 23 Why Use Multiplexing ......................................................................... 24

Applications of Multiplexing ............................................................ 24 Benefits of Multiplexing ................................................................... 24

Multiplexing ......................................................................................... 25 ECU Communication .......................................................................... 26 Signaling Between ECUs .................................................................... 27 Communication Protocols ................................................................... 28 Multiplex Topology .............................................................................. 29

Ring Topology ................................................................................. 30 Two Opens in a Ring Network ........................................................ 31 Open in a Star Network .................................................................. 32 Open in a Bus Network ................................................................... 33

Single Wire vs. Twisted-Pair ............................................................... 34 Advantage of Twisted-Pair Wiring .................................................. 35

Section 3: Signals &

Waveforms

Section 3 Topics ................................................................................. 37 Electronic Communication .................................................................. 38

Types of Waveforms ....................................................................... 38 Waveform Measurements ................................................................... 39

Amplitude ........................................................................................ 39


ii Technical Training

Frequency ....................................................................................... 40 Pulse Width ..................................................................................... 41 Duty Cycle ...................................................................................... 42

Section 4: Measuring

Signals

Section 4 Topics ................................................................................. 43 The Oscilloscope ................................................................................ 44 PC Oscilloscopes ................................................................................ 45 Basic Operation .................................................................................. 46 Oscilloscope Scales ............................................................................ 47

Repair Manual Suggested Scales .................................................. 48 Repeating vs. Changing Patterns ....................................................... 49 Capturing Waveforms ......................................................................... 50 Scope Pattern Comparison ................................................................. 51 The Effect of Scale .............................................................................. 52 Trigger Function .................................................................................. 53 Other Trigger Uses ............................................................................. 54 Advanced DVOM Features ................................................................. 55

MIN/MAX Recording ....................................................................... 55 Peak MIN/MAX ............................................................................... 55 Relative Delta ................................................................................. 55 Frequency Measurement ................................................................ 56 Duty Cycle ...................................................................................... 56

Worksheet: DVOM Set-up & Advance Features ................................. 57 Instructor Demo: Using DVOM Resistance Setting ............................ 58

Section 5: Using a PicoScope™

Section 5 Topics ................................................................................. 59 Introduction to PicoScope™ ................................................................ 60

Connecting the Leads ..................................................................... 60 PicoScope Features ........................................................................... 61

Auto Voltage Scale ......................................................................... 61 Auto Setup ...................................................................................... 61 Manual Voltage Scale Settings ....................................................... 62 Manual Time Scale Settings ........................................................... 62 Turning the Trigger On ................................................................... 63 Setting the Trigger .......................................................................... 64 Start and Stop Capturing ................................................................ 65 Horizontal Zoom ............................................................................. 66 Rulers ............................................................................................. 67 Sample Rate ................................................................................... 69 Displaying Two Channels ............................................................... 70 Separating the A-B Traces ............................................................. 71 Printing, Saving and Sending Patterns ........................................... 72

Worksheet: In-class PicoScope: Basic Set-up .................................... 73 Worksheet: Using DVOM & PicoScope .............................................. 74 Instructor Demo: PicoScope & Power Window Circuit ....................... 74


Technical Training iii

Section 6: Using an Inductive

Clamp

Section 6 Topics ................................................................................. 75 The Inductive Clamp ........................................................................... 76

Polarity ............................................................................................ 76 Current Rating ................................................................................ 77 Preparation for Use ......................................................................... 78 Converting Measurements to Amps ............................................... 79

Amp Clamp Applications ..................................................................... 80 Diagnosing Short Circuits and Parasitic Draw ................................ 80 Diagnosing Motor Faults with an Oscilloscope ............................... 81

Worksheet: Inductive Current Clamp I: Measurement & Conversion . 82 Worksheet: Inductive Current Clamp II: A/C Blower Motor ................. 82

Section 7: Multiplex Circuit

Diagnosis

Section 7 Topics ................................................................................ 83 Additional Properties of MPX Protocols .............................................. 84

Communication Direction ................................................................ 85 Transmission Timing ....................................................................... 86 Collision Detection .......................................................................... 87 Data Casting ................................................................................... 88 Sleep Mode ..................................................................................... 89 Wakeup Function ............................................................................ 89

Body Electronics Area Network .......................................................... 90 Local Interconnect Network ................................................................ 91

LIN Characteristics ......................................................................... 91 LIN Replacing BEAN ...................................................................... 91 LIN Gateway Function .................................................................... 92

Controller Area Network ...................................................................... 93 Terminating Resistors ..................................................................... 93

Audio Visual Communication-Local Area Network ............................. 94 AVC-LAN Protocol .......................................................................... 95

Gateway ECU ..................................................................................... 96 CAN Gateway ECU ........................................................................ 96 Summary of Gateway ECU Functions ............................................ 97 CAN Gateway ECU Functions ........................................................ 98

Transmit/Receive Charts .................................................................... 99 BEAN Signal ..................................................................................... 100 BEAN Diagnosis ............................................................................... 101

Open Circuit .................................................................................. 102 Short Circuit .................................................................................. 103 Short Circuit Step 1........................................................................ 104 Short Circuit Step 2........................................................................ 105 Short Circuit Step 3........................................................................ 106 Short Circuit Step 4........................................................................ 107 Short Circuit Step 5........................................................................ 108 Short Circuit Step 6........................................................................ 109 Diagnosing a Large Network ........................................................ 110 Diagnosing with Techstream ........................................................ 111 Diagnosing a BEAN Open Circuit with an Oscilloscope ............... 112


iv Technical Training

Worksheet: BEAN Network Diagnosis .............................................. 113 Instructor Demo: BEAN Operation and Diagnosis ............................ 113 LIN Signal ......................................................................................... 114 LIN Diagnosis .................................................................................... 115 Worksheet: A/C LIN Interface ........................................................... 116 CAN Signal ....................................................................................... 117 CAN Diagnosis ................................................................................. 118

Short Between CANH and CANL ................................................. 118 Short to B+ or Ground ................................................................... 118 Opens ........................................................................................... 119 CAN Bus Check ............................................................................ 120 Location of DLC3 .......................................................................... 120 Terminating Resistors ................................................................... 121 Resistance Tests on CAN Circuits ................................................ 122

Worksheet: CAN Diagnosis ............................................................. 124 Instructor Demo: CAN Resistance Test Precautions ........................ 124 Worksheet: CAN Main Bus Faults ................................................... 125 Worksheet: CAN Sub Bus Diagnosis ............................................... 125 AVC-LAN Signal ............................................................................... 126 AVC-LAN Diagnosis .......................................................................... 127

AVC-LAN DTCs ............................................................................ 128 Worksheet: AVC-LAN Inspection ...................................................... 129 Other Multiplex Circuits ..................................................................... 130

A/C Servo Motor Circuits .............................................................. 130 BUS Connectors ............................................................................... 131 Pulse-Type Servo Motors ................................................................. 132 Worksheet: A/C Bus Servo Motor Operation & Diagnosis ................ 133

Section 8: Electronic

Systems

Section 8 Topics ............................................................................... 135 Engine Immobilizer Function ............................................................ 136 Engine Immobilizer Operation .......................................................... 137 Key Code Registration ...................................................................... 137 Master Keys and Sub Keys .............................................................. 138 Automatic Key Code Registration ..................................................... 139

Watch for Error Codes .................................................................. 139 Ending Automatic Registration ..................................................... 139

Configuration in Earlier Models ......................................................... 140 Configuration in Later Models ........................................................... 141 Immobilizer Reset ............................................................................. 142 Immobilizer Reset Support Chart ...................................................... 143 ECU Communication ID Registration ............................................... 144 Be Wary of Differences between Models .......................................... 145 Analyzing ECU Input and Outputs .................................................... 146

Transponder Signals ..................................................................... 147 Power and Ground Circuits ........................................................... 148 Terminal Values and Conditions ................................................... 149


Technical Training v

Transponder Key Amplifier Terminal Values ................................. 150 ECM Terminal Values ................................................................... 151

Worksheet: Immobilizer .................................................................... 152 Power Distributor ............................................................................. 153

Protect Mode ............................................................................... 153 Mode Monitor Terminal ................................................................ 153

Smart Junction Box (MICON) ........................................................... 154 High Intensity Discharge (HID) Headlights ....................................... 155 Dynamic Laser Cruise Control Operation ......................................... 156 Laser Sensor ..................................................................................... 157 Indicators ......................................................................................... 158 Error/Cancellation Codes .................................................................. 158 Constant Speed Control .................................................................... 159 Decelerator Control............................................................................ 160 Follow-Up Control .............................................................................. 161 Accelerator Control ........................................................................... 162 System Diagram ............................................................................... 163 Distance Control ECU Waveforms .................................................... 164 Laser Radar Sensor Waveforms ....................................................... 165

Appendix Appendix ........................................................................................... 167 Transistors ........................................................................................ 168

Transistor Types ........................................................................... 169 How a Transistor Works ............................................................... 170 Transistor Switches ...................................................................... 171 Transistor Amplifiers ..................................................................... 172 Digital Circuits ............................................................................... 173 Analog-to-Digital Converter .......................................................... 174

Logic Gates ....................................................................................... 175 Normal CAN Signal ........................................................................... 176 CAN Shorts and Opens .................................................................... 177

Short CANH to CANL ................................................................... 177 Short CANH to B+ ......................................................................... 178 Short CANL to B+ ......................................................................... 178 Short CANH to Ground ................................................................. 179 Short CANL to Ground .................................................................. 179 Open in CANH or CANL (Main Bus) ............................................. 180 Open in CANH and CANL (Main Bus) .......................................... 181

BEAN Signals ................................................................................... 182 BEAN Short to Ground ................................................................. 183

Normal BEAN, Dual Trace ................................................................ 184 BEAN Open Circuit, Dual Trace ................................................... 185

Worksheets


vi Technical Training

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Objectives

673 Electronic & Computer Controlled Systems

Technical Training a

Course 673 Electronic & Computer Controlled Systems

Final Student Performances

Terminal Objective (Terminal FSP)

Given all of the applicable tools, equipment, and appropriate vehicles, the technician will be able to apply a number of diagnostic techniques to monitor and repair faults in advanced computer and electronic circuits.

Technician Objectives (FSPs)

The technician will be able to:

1. Research information related to:

• The purpose and function of ECU terminals

• Inputs & Outputs

• Terminals of the ECU

• Power & Ground points

2. Identify inputs and outputs and determine how they affect ECU operation.

3. Differentiate between:

• Pulse width & duty cycle

• Frequency & duty cycle

4. Identify the consequences of the following to the diagnostic process:

• Initialization (Memory Loss)

• Customization (CBEST)

• Sleep mode vs. normal operation

5. Demonstrate proficient use of the advanced DVOM features.

• MIN/MAX function

• Peak MIN/MAX function

• Measure frequency

• Measure duty cycle

6. Apply advanced DVOM functions for quick diagnostic evaluations.

7. Practice using an Inductive Current Clamp with a DVOM to provide the ability to take current readings without breaking into a circuit.

8. Utilize an inductive Current Clamp to evaluate system operation & determine diagnostic strategy.

9. Practice conversion of voltage and amperage values to apply to inductive clamps that use conversion factors for sensitivity.

10. Monitor AC blower motor current using a DVOM equipped with an inductive current clamp, and monitor current using an oscilloscope and inductive clamp.

Objectives


b Technical Training

11. Properly set-up an oscilloscope

• Auto features

• Voltage & Time Scale Settings

• Horizontal & vertical rulers

• Trigger point

• Horizontal & vertical zoom features

12. Apply the basic features of the oscilloscope used in combination with the Techstream Unit.

13. Locate and back probe a dimmer-controlled interior lamp or LED, practice measuring Voltage (V), Hertz (Hz), and percentage values (%) using a DVOM, and use an oscilloscope to display the signal pattern.

14. Set oscilloscope voltage and time settings appropriate to the circuit measured.

15. Utilize oscilloscope patterns derived from a known good vehicle to verify normal system operation.

16. Differentiate between different oscilloscope patterns.

17. Use an oscilloscope to confirm proper operation vs. a faulty circuit

• Duty cycle

• Frequency

• Amplitude

18. Use an oscilloscope to identify intermittent faults.

19. Capture, record, save and send oscilloscope waveforms.

20. Identify Body Electronics Area Network topology and network operation.

21. Perform fault diagnostics on a BEAN network.

22. Identify Local Area Network topology and network operation.

23. Monitor and diagnose the AC Control Assembly operation and LIN communication using Techstream, an oscilloscope and TIS.

24. Identify Controller Area Network topology and network operation.

25. Use an ohmmeter and an oscilloscope to observe CAN High and CAN Low; diagnose a short to ground and an open circuit on CAN High and CAN Low; and short CAN High to CAN Low to observe the results.

26. Develop a strategy to diagnose a CAN Network fault using the EWD, a Techstream CAN Bus Check, and the information provided.

27. Identify Audio Visual Communication-Local Area Network topology and network operation.

28. Create, monitor and diagnose an AVC-LAN System amplifier malfunction using Techstream and an oscilloscope.

29. Monitor AC bus and servo motor operation using Techstream DATA LIST and an oscilloscope to deduce communication problems with the AC System.

30. Reference service literature to determine if immobilizer reset is supported on a vehicle.

31. Use Techstream Data List to make determinations related to the ID Code of the transponder chip embedded in the ignition key of the Immobilizer System.

32. Use an oscilloscope to observe Immobilizer System waveforms under varying conditions and compare them to those found in the Repair Manual.

Technician Handbook673 Electronic & Computer Controlled Systems


Welcome Toyota Technicians

Technical Training 1


Technical Training2

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Course Menu

• Electronic Control Units• Overview of Multiplex Communication• Signals & Waveforms• Measuring Signals• Using a PicoScope™• Using an Inductive Clamp• Multiplex Circuit Diagnosis• Electronic Systems

Electronic & Computer Controlled Systems

• Transistors• CAN Waveforms• BEAN Waveforms

A Appendix



Technical Training4




• Electronic Control Units• Logic Function • Simple ECU Inputs• Simple ECU Outputs• Self-Diagnosis• Memory• Customization• Initialization

Section 1 Topics

Electronic Control Units



Electronic Control Units (ECUs) are small computers programmed to perform specific automotive functions.

ECUs use electronic components in integrated circuits to perform their functions.

What are some typical automotive ECUs?

In the 1970’s, the decreasing cost and increasing power of computerized microprocessors launched the personal computer industry. Because of their speed and flexibility in carrying out complex functions, microprocessors were adapted for hundreds of uses beyond personal computers. The first microprocessors began appearing in automotive engine control systems in the early 1980s. In automotive applications, they became known as electronic control units (ECUs). Today, some vehicles may have dozens of ECUs controlling a wide variety of vehicle systems, including:• engine controls• transmission• braking• steering • air conditioning• door locks• suspension• cruise control• tire pressure monitoring• and many other systems.


Technical Training6



ECU Logic Function

ECUs have electronic logic circuits that “make decisions”by evaluating conditions according to predetermined rules.

Light Control SW

Light Control Sensor

Headlights

Taillights

Body ECU

Con

ditio

nsD

ecis

ion

IFLight control switch is in the AUTO position

andLight control sensor detects LOW ambient light

andIgnition switch is ON

THENTurn headlights ONTurn taillights ON

An ECU is a small computer programmed to perform a specialized function in the vehicle. As with any computer, it operates on the principle of input, processing, and output.Input – Information about conditions is supplied to the ECU as input signals. Input can be provided by:• sensors• switches• other ECUs.Processing – The ECU analyzes the input signals. Based on its programming, it determines what output signals to send, if any.Output – Vehicle systems are controlled by the ECU output signals. Thesesignals may cause a motor to operate, a light to come on, or some other operation of a vehicle component.

For an example of the ECU’s logic function, consider the lighting control system which is within the Body ECU. A simple lighting control system uses three inputs – the light control switch, the light control sensor, and the ignition switch.When the condition of these three inputs matches the conditions preprogrammed in the ECU, the ECU turns on the headlights and taillights.

Logic Function

How ECUs Work


Simple ECU Inputs

Variable Resistance

What are some other types or examples of ECU inputs?

Temp Sensor

Combination Switch

Voltage ON/OFF

Oxygen Sensor

Variable Voltage

Voltage Pulse Pattern

Active Speed Sensor

MRE A

MRE BSensor IC

Exhaust Gas

Signals from switches and sensors can supply information to the ECU in several ways.Voltage ON/OFF – A simple switch opens or closes a circuit. It is the presence or absence of voltage in the circuit that signals the ECU. Variable Voltage – Some sensors produce a voltage that changes depending on the conditions the sensor is measuring. The amount of voltage produced at any given moment provides information about the condition at that time.Variable Resistance – In other types of sensors, electrical resistance increases or decreases as external conditions change. Sensing the changing voltage as a result of changing resistance in the circuit signals the ECU what the conditions are.Variable Pulse Pattern – Another method for signaling the ECU about changing conditions is to turn a circuit on and off rapidly at a particular frequency. This works especially well for signaling rotational speed. It is the frequency of the ON/OFF pulses that supplies information to the ECU.

Simple ECU Inputs

Technical Training8



Voltage ON/OFF (Switch) Input

12.6V 12.6VECU ECU

OFF: V = 12.6V(open circuit voltage)

Ground-side switched

ON: V = 0.1V(available voltage)

Voltage can also be measured at the ECU terminal.

The ECU detects the state of a ground-side switch by reading the circuit voltage. When switch ON is detected, the ECU performs a function, such as turning on a lamp.

B+ B+

12.6v 0.1v *

* Conceptual illustration only

* 5V0V

The diagrams above illustrate a ground-side switch connected to an ECU. The ECU supplies battery voltage to the switch circuit and provides the circuit’s load (a resistor). The ECU’s electronic circuits detect when the voltage after the load is high (near battery voltage) or low (near ground voltage).While the switch is open, no current is flowing and the available voltage after the load is near battery voltage. When the switch is closed, current flows and most of the battery voltage is dropped across the load. The available voltage after the load is now near ground voltage.In this example, the switch controls a lamp, but is not actually part of the lamp circuit. When the ECU senses a voltage drop in the switch circuit, it supplies five volts to the transistor. This in turn closes the lamp circuit, lighting the lamp.

You can detect the same high or low voltage the ECU is detecting by measuring voltage at the appropriate ECU terminal. If the switch is closed and the voltage remains high, you’ll know there is an open in the circuit between the ECU and the switch.

The actual wiring inside the ECU is extremely complex. The ECU circuit details shown in the diagrams above and the diagrams on the following pages are to illustrate concepts, not actual internal connections.

Voltage ON/OFF (Switch) Input

NOTE

SERVICE TIP


ECM

Variable Voltage Input

The oxygen sensor is a voltage generator.

V > 0.45v : air-fuel ratio too rich

V = 0.45v : air-fuel ratio correct

V < 0.45v : air-fuel ratio too lean

Atmosphere

Voltage

The engine control module interprets the voltage to make corrections to the air-fuel ratio.

V

Exhaust Gas

An oxygen sensor is a voltage generator, producing between 0.1v and 0.9v depending on the oxygen content of the exhaust gas compared to the atmosphere.

The engine control module’s electronic circuits measure the amount of voltage generated by the oxygen sensor, and use that information to control the air-fuel ratio.

Variable Voltage Input

Technical Training10



Variable Resistance Input

A temperature sensor is a type of variable resistor.Its resistance changes with temperature.

12.6V or 5VAn ECU can detect the change in the sensor’s resistance by measuring voltage.

ECU

V

A temperature sensor is a type of variable resistor whose resistance changes with temperature. This type of sensor is often called a thermistor.Two types of thermistor are:Positive temperature coefficient (PTC) thermistor – resistance increases as temperature increasesNegative temperature coefficient (NTC) thermistor – resistance decreases as temperature increasesThermistors are commonly used for engine coolant temperature sensors and ambient temperature sensors. Modern Toyota vehicles use NTC thermistors exclusively.

Variable Resistance Input


Pulse Pattern Input

An active wheel speed sensor generates a series of voltage pulses as the wheel rotates. As rotation speed increases, pulses are generated at a higher frequency.

Lower Rotation Speed

Voltage

Time

Voltage

Time

Higher Rotation Speed

The ECU measures the pulse frequency to calculate vehicle speed.

MRE A

MRE BSensor IC

Another type of ECU input is a pulse pattern. When voltage risesmomentarily, then falls, the transient voltage reading is called a pulse. When a component creates multiple pulses, the result is a pulse pattern (or pulse train).An active wheel speed sensor is a component that generates a pulse pattern. A magnetic ring mounted on the wheel hub has alternating north-south fields that are detected by the sensor pickup. As the wheel rotates, the alternating magnetic fields are converted into a series of voltage pulses. The frequency of the pulses increases with the wheel rotation speed. When the pulse pattern is provided as ECU input, the ECU’s circuits are able to measure the pulse frequency and calculate wheel RPM and vehicle speed.

Pulse Pattern Input




See Appendix for More InfoAA

Simple ECU Outputs

When the operating conditions are met, the ECU makes a connection to power or ground to energize a circuit

B+

ECU

Transistor

Ground-side controlled circuit

Power-side controlled circuit

Collector

Base

Emitter

How a Transistor Works (NPN)

When voltage is applied to the base…

...current can flow from the collector to the emitter

ECU

B+

5V

PNP

NPN

The simplest way for an ECU to control a vehicle function is to turn a circuit on or off. A circuit can be ground-side switched or power-side switched.

Electronic circuits use transistors for switching circuits on and off. A transistor is a solid-state electronic component having a base, collector and emitter. In the more commonly used NPN transistor, when sufficient voltage is applied to the base, current flows from the collector to the emitter.

One of the advantages of the transistor is that a low voltage at the base is able to control a large current flowing through the collector and emitter. In that respect, a transistor is similar to a relay.

Some transistors also regulate current flow based on the amount of voltage applied to the base. Within the transistor’s limits, a higher base voltage results in a greater flow of current through the collector/emitter. This feature is used in amplifier circuits where the low voltage signal from a microphone regulates current flow in higher power speaker circuits

Simple ECU Outputs

Transistors as Switches


Pulse Width ModulationThe ECU can open and close a circuit rapidly to control component operation. The process of varying the amount of time a circuit is ON is called pulse width modulation.

The ECM regulates the injector ON time by regulating the width of the voltage pulse to the injectors.

Notice the pulse width increases at higher load as the ECM increases the injector ON time.

Voltage Pulses

Example

Pulse Width

An ECU’s electronic circuits have the ability to open and close a circuit very rapidly. The ECU can switch a circuit on for a fraction of a second at very precise intervals.When a circuit is switched ON and then OFF, the momentary change in voltage creates a voltage pulse. (The pulse can be either a momentary increase or decrease in voltage depending on whether the circuit is ground-side switched or power-side switched and where the voltage is measured.)When the voltage is viewed on an oscilloscope, the voltage pulse’s width represents the amount of time the circuit is switched ON and can be as brief as 1 millisecond or less. In some circuits, the ECU uses the amount of ON time to regulate component operation. When the ECU varies the width of the voltage pulse (the ON time) to control a component, the process is called pulse-width modulation.

In the above example, the frequency of the pulses changes as well as the pulse width. In some circuits, the frequency of the pulses is constant.

Pulse Width Modulation


NOTE


Measuring Duty CycleWhen the ECU modulates a circuit at a constant frequency, you can measure the circuit’s duty cycle. Duty cycle is the percentage of ON time compared to total cycle time.

B+

ECU

12 V

75% ON (grounded)

0 V

Varying the duty cycle can vary the brightness of a lamp or the speed of a motor.

12 V

0 V

If the percentage of ON time decreases, the lamp becomes dimmer.

In a ground-side controlled circuit,

measure after the load.

5V

1 cycle(100%)

25% ON (grounded)

1 cycle(100%)

The terms pulse-width modulation and duty cycle are often confused or used incorrectly.Pulse-width modulation is a function an ECU can perform to turn a circuit on and off rapidly to regulate the amount of ON time. As the pulse width changes, the frequency of the pulses might or might not change depending on the circuit design and intended operation.When a circuit is switched on and off rapidly at a constant frequency, duty cycle measures the percentage of ON time compared to total cycle time. If the circuit is ON 75% of the time, it is operating at a 75% duty cycle. When a circuit is duty-cycle controlled, the pulse frequency does not change – only the percentage of ON time. An ECU varies the duty cycle to control the speed of a motor or the brightness of a lamp by switching the circuit ON and OFF hundreds of times per second. Human senses can’t perceive a lamp or motor being cycled on and off that quickly. Nonetheless, the amount of power to the component increases or decreases depending on how much of the time the circuit is ON versus OFF. As OFF time increases, the net power supplied to a component decreases resulting in the lamp becoming dimmer or the motor running slower. As ON time increases, power increases and the lamp becomes brighter or the motor runs faster.

When the circuit is ground-side controlled, voltage before the load is always battery voltage, and voltage after the switch is zero, or near zero. To observe voltage modulation, place the positive probe between the load and the switch (which may be an ECU).

Duty Cycle

NOTE



Measuring Duty CycleSignals in a power-side controlled circuit are the opposite of signals in a ground-side controlled circuit.

75% ON (powered)

In a power-side controlled circuit,

measure before the load.

B+

If the percentage of ON time decreases, the lamp becomes dimmer.

25% ON (powered)

1 cycle(100%)

1 cycle(100%)

ECU

Most circuits in Toyota vehicles are ground-side controlled. When a pulse-width modulated circuit is power-side controlled, the voltage modulation is observable after the ECU and before the load. In this arrangement, the circuit is ON when the voltage rises. Note that if voltage is measured after the load, a very minute change in voltage occurs as the circuit is modulated. At this point in the circuit, voltage is zero when the circuit is open. When the circuit is closed, ground voltage is present. The difference is usually less than 0.1V and may not be observable depending on your scope settings.

Power-Side Control




Self-Diagnosis

The ECU’s internal wiring can be arranged so it can detect when an input circuit is open or shorted to ground.

Throttle Position Sensor

ECM

VTA

VTA2

VC

E2

Under normal conditions, the ECM senses more than 0V and less than 5V at VTA and VTA2.

5V

2002 Tundra V8

DTC P0120 Throttle/Pedal Position Sensor/Switch “A”Circuit Malfunction

With either a short or an open in the input circuit, voltage at VTA and VTA2 becomes 0V and the ECU sets a DTC.

A significant reason ECUs have become so common in automobile systems is their ability to perform self-diagnosis. ECUs can identify faults in circuits, components, and even within the ECU itself. When a fault is detected, the ECU can: • Illuminate a warning light• Set a diagnostic trouble code• Begin operating in a fail-safe mode by:

Disabling a system that is working incorrectly Using sensor data from alternate sources Applying alternate rules for operating the vehicle or subsystem

to maintain maximum safety

An ECU’s self-diagnosis capabilities can range from very simple to highly sophisticated. Each ECU has its own features and limitations, and very few work in exactly the same way.The example above is a throttle position sensor circuit. The electronics inside the engine control module (ECM) are designed so that an open or a short to ground on VTA or VTA2 can be detected and a DTC set. The circuit arrangement inside the ECM is not able to distinguish a short from an open, however. In either case, the voltage the ECM is monitoring goes to 0V.

Self-Diagnosis

Differences in Self-Diagnosis



ECM

VTA1

VTA2

VC

E2

5V

Self-Diagnosis

ECUs can be wired so they can detect the difference between an open or short, and set a different DTC for each.

DTC P0122 Throttle/Pedal Position Sensor/Switch “A”Circuit Low Input

DTC P0123 Throttle/Pedal Position Sensor/Switch “B”Circuit High Input 2003 Tundra V8

What is the normal voltage at VTA2?

In this arrangement, what is the normal voltage at VTA1?

What is the voltage with a short in the circuit?

What is the voltage with an open in the circuit?

In this throttle position sensor circuit, the electronics inside the ECM are arranged slightly differently. In this arrangement, a short to ground on a VTA line causes the monitored voltage to go to 0V. An open in a VTA line, however, causes the monitored voltage to go to 5V.Thus, this ECM can distinguish between an open or short on an input circuit and can set a DTC for one or the other. The additional data supplied by the ECM makes it easier and faster to diagnose and correct the problem.

Differences in Self-Diagnosis (Cont’d)




Like other computers, ECUs have internal memory. Besides storing DTCs, they can also store switch settings and component positions. Over time, ECUs can acquire and store information about the vehicle’s operating characteristics and driver/occupant preferences. The data stored in memory can have a direct affect on how well the vehicle operates and the driver’s perceptions of comfort and convenience.

Volatile memory chips are the type that require constant power to maintain what is stored in them. When the power is removed, their memory contents are erased. These types of memory chips are used for ordinary microprocessor memory. (RAM for example.)Non-volatile memory chips retain their contents even when the power is removed. These types of memory chips permanently store the microprocessor’s operating instructions, or logic. (ROM for example.)Programmable Read Only Memory (PROM) – A memory chip that can be programmed once, but cannot be reprogrammed.Erasable Programmable Read Only Memory (EPROM) – A programmable chip that can be removed from its circuit and reprogrammed.Electrically Erasable Programmable Read Only Memory (EEPROM) – A programmable chip that can be electrically erased and reprogrammed without removing it from the circuit.

ECU Memory

• DTCs• Driver preferences

• Vehicle operating characteristics

ECUs have different types of memory.

B+ ECU Memory

RAM(volatile)

ROM(permanent)

EEPROM(reprogrammable)

ECU program logic

ECU program logic, data (reflash)

Types of ECU Memory

ECU Memory


ECU Customization

Because ECUs have memory, they can be programmed with owner/driver preferences.

Main Body ECU Would you like the interior light turned ON when the doors are unlocked?

Would you like the interior light turned ON when the ignition is turned OFF?

How long would you like the interior lights to be left ON?

ECU Memory

A. Yes

B. Yes

C. 30 seconds

ABC

No matter how carefully automobile manufacturers analyze the features that new car buyers want, there will always be those who want a feature to work differently. ECUs have made it much easier for owners to customize many of the vehicle’s convenience features to suit their own preferences.The settings for customizable features are stored in ECU memory. Needless to say, if the memory is lost then any preferences the owner has chosen are also lost. Memory can be lost when the ECU loses its connection to the battery, and also when the ECU is replaced.

Before disconnecting the battery, make note of the owner’s customized settings and restore those settings when service is complete.

When one driver changes a customized setting without informing other drivers, another driver may view the change in operation as a malfunction. Be sure to consider the potential role of customized settings on a customer’s concern before beginning a problem diagnosis.

Customization

SERVICE TIP

NOTE




ECU Initialization

Initialization procedures can be very different depending on the ECU.

• Unload the vehicle

• Jumper terminals 4 and 8 of DLC3

• Flash the headlights 3 times

Headlamp Leveling ECU Initialization

Driver’s Door Power Window Initialization (Body ECU)

• Turn ignition ON

• Hold the switch to open the window

• Hold the switch to close the window

• Keep holding the switch until the switch stops blinking

Examples

Completely Closed

ECUs may need to be initialized when: • A new ECU is installed• Key components related to the ECU’s operation have been replaced• Loss of power erases critical memory settings.Initializing an ECU simply means preparing it for operation. If an ECU is not initialized when required:• The system may be inoperable or operate incorrectly• Some system features may be disabled.

When an ECU is installed, it becomes part of a system of interconnected components. Many ECUs are designed to work in systems with optional components in sometimes varying configurations. Before the ECU can begin operation, it must learn the configuration of the system it’s connected to, and sometimes obtain data from other components.This takes place during initialization. When initialization is completed, the ECU has acquired the information it needs to begin performing its function.In quite a few vehicle systems, ECUs control motors, such as power window motors and power back door motors. These systems require initialization in particular so the ECU can synchronize itself with the motor to control the opening and closing function properly. In systems with jam protection, this feature may be inoperable until the ECU has been initialized.

Before determining an ECU is faulty, first verify that it doesn't just need to be initialized.

Initialization

Why Initialize?

NOTE





• Why Use Multiplexing?• How ECUs Communicate • Communication Protocols• Multiplex Topology• Single Wire vs. Twisted Pair

Section 2 Topics

Overview of Multiplex Communication



Why Use Multiplexing?

One multiplex circuit does the work of many conventional circuits.• Fewer wires • Lighter wiring harnesses• Simpler, more reliable wiring• Fewer components• Fewer connections• Lower cost• Self diagnostics

Multiplexing (or MPX) is a method for communicating between multiple components over a single one-wire or two-wire communication line.Without multiplexing, inter-module communication requires dedicated, point-to-point wiring between all components resulting in bulky, expensive, complex, and difficult-to- install wiring harnesses. Using multiplexing reduces the number of wires by combining many signals on a single wire. Control modules use the data received to control functions such as anti-lock braking, turn signals, power windows, dashboard displays, and audio systems.

In-vehicle networking provides a number of benefits:• Each function requires fewer dedicated wires, reducing the size of the

wiring harness. This yields improvements in system cost, weight,reliability, serviceability, and installation cost.

• Common sensor data, such as vehicle speed, engine temperature, etc. are available on the network, so data can be shared, thus eliminating the need for redundant sensors or multiple connecting wires.

• Networking allows greater vehicle flexibility because functions can be added through software changes in the ECU. Without multiplexing,systems require an additional module or additional terminals for each function added.

Benefits of Multiplexing

Applications of Multiplexing



What is Multiplexing (MPX)?

Multiplexing is a way to use one wire to communicate between many devices. Conventional wiring between components

MPX communication

line

Discrete signals

Light

Motor

Heater

SolenoidSwitch

Light

Motor

Heater

SolenoidSwitch

ECUECU

L M H S

In conventional electrical circuits, each voltage signal between components requires its own dedicated wire. The presence, absence, or amount of voltage on the wire (supplied by a switch or a sensor, for example) controls the operation of a component on the other end.In a multiplex circuit, a computer chip on one end of a single wire can transmit a series of coded voltage signals that can be interpreted by a computer chip on the other end. The computer chips are inside electronic control units (ECUs), and the coded voltage signals are data packets.A data packet may instruct the receiving ECU to:• Turn on a light• Start a power window motor• Activate a solenoidBecause the data packets are sent in series, multiplexing is also referred to as serial communication or serial networking, and the communication line is called a serial data bus.

Multiplexing



How ECUs Communicate

ECU Logic Circuit:

To communication line:• Supply voltage when transistor is OFF• Ground voltage when transistor is ON

• Controls the ON/OFF signal • “Reads” the data on the MPX line• Performs self diagnosis

ECU

Time

Voltage

0 v

ECUs communicate by sending voltage pulses in a coded sequence.

Supply

In the ECU, a switching transistor in the logic circuit controls the transmitting of multiplex signals. When the transistor is OFF, no current flows. Referring to the diagram above, if you were to measure the available voltage on the communication line, you would find supplied voltage.When the transistor is turned ON, current flows and all of the available voltage is dropped across the resistor. Now the voltage measurement on the communication line (after the resistor) is ground voltage.By turning the transistor ON and OFF in a timed sequence, the ECU can send a message to another ECU, similar to sending a message in Morse code. Part of the message, called a data packet, indicates which ECU the message is addressed to. Other ECUs listening to these messages ignore the ones not intended for them.

The ECU communication line is powered through a resistor that acts as a load in the circuit. This is commonly called a pull-up resistor. If the circuit is grounded, the resistor protects the ECU from damage.

ECU Communication

NOTE



Signaling Between ECUs

Sender Supplies B+

Receiver Supplies B+

Sends signal

ECUECU

12V

ECUECU

When one ECU signals another, the one sending the signal is not necessarily the one supplying the power to the circuit.

Sends signal

12V

In diagnosing ECU controlled circuits, don’t make the assumption that the ECU sending a signal is the one supplying the circuit voltage. As shown in the illustrations above, it’s possible for the ECU receiving a signal to be the one providing power to the circuit.

Signaling Between ECUs



Protocol BEAN(TOYOTA Original)

CAN(ISO Standard)

LIN(Consortium)

AVC-LAN(TOYOTA Original)

Application Body Electrical Power Train Body Electrical Audio

Communication Speed 10 kbps 500 kbps (HS)*

250 kbps (MS) 20 kbps 17.8 kbps

Communication Wire AV Single Wire Twisted-pair wire AV Single Wire Twisted-pair wire

Drive Type Single Wire Voltage Drive

Differential Voltage Drive

Single Wire Voltage Drive


Voltage 10+ volts 2.5v to 3.5v CANH2.5v to 1.5v CANL 8 volts 2v to 3v TX+

2v to 3v TX-

Configuration Ring/Daisy Chain Bus Star Star

Sleep/Wake-up Available Available Available N.A.

Communication ProtocolsA “protocol” is the set of rules and standards for communication between components.

BEAN: Body Electronics Area NetworkCAN: Controller Area NetworkLIN: Local Interconnect Network

AVC-LAN: Audio Visual Communication - Local Area Network

* Up to 1 Mbps

The rules and standards for transmitting and receiving data packets between ECUs are called a protocol. Some protocols provide faster exchange of messages between components and more reliable operation than others. As speed and reliability increases, so does the cost.

The chart above compares some of the characteristics of the different protocols found in Toyota vehicles.

• BEAN is the earliest protocol used by Toyota. Based on early technology, it is also one of the slowest protocols. BEAN is typically used for body electrical systems such as lights, locks, windows, and air conditioning.

• AVC-LAN is another early protocol developed by Toyota as a faster alternative to BEAN for audio, video, and navigation components.

• CAN, the ISO standard for automotive applications, is a high-speed protocol for critical vehicle systems such as engine control, braking, pre-collision, and SRS systems.

• LIN is an alternate, low-speed standard protocol developed in later years and used by many manufacturers. Because it is a common standard, it is slightly lower in cost, and because it is a newer standard, it is slightly faster than BEAN. In later model Toyota vehicles, LIN replaces BEANfor control of some body electrical systems such as windows and seats.

Network speeds are measured in bits per second (bps). A “bit” (represented as ON or OFF, or 0 or 1) is the smallest unit of the code used in a data packet. Kbps stands for kilobits (1000 bits) per second. Mbps stands for megabits (one million bits) per second.

Communication Protocols

NOTE



Multiplex Topology

Star Style Each ECU is connected directly to a master ECU with a central control function.

Bus StyleAll ECUs are connected to a single

common communication line.

Daisy Chain StyleThe ECUs are connected in a combination

ring and bus form.

Applies to CAN

Applies to LIN and AVC-LAN

Applies to BEAN

ECU ECU ECU

ECU

ECU

ECU

ECU

ECU

ECUECU

ECU

ECU

Master ECU

ECU

ECU

ECU

Topology describes the pattern of physical connections between components on a network. This may also be called network architecture.Multiplex networks can be configured in a variety of designs. Toyota networks are arranged using primarily three styles: the bus, the ring, and the star.

• Bus. In the bus style, multiple ECUs are connected to a single commoncommunication line, allowing each ECU to transmit or receive signals directly with any other ECU on the network.

• Ring. ECUs connected in a ring have two network lines to provide a backup path for communication. If one communication line is disconnected, the ECU can still receive network communications on the other line.

• Star. The star style uses a central ECU called a master to control the other ECUs in the network (slaves). In this configuration, slaves cannot communicate directly with one another without passing the message through the master.

• Daisy Chain. Sometimes a multiplex circuit can combine two design types. An example is a BEAN circuit with both ring and bus topologies.

Components on a network are referred to as nodes. ECUs are not the only possible nodes. Sensors with multiplex communication capability can also be nodes on a network. Examples are steering angle sensors and yaw rate sensors.

Multiplex Topology

NOTE



Ring Topology

In a ring network, a single open circuit in the loop does not affect performance.

Communication lines (bus)

One open wire does not affect network operation.

When network components are connected in a ring, every component has two paths for sending messages to another component. The advantage of ring topology is added reliability because the network continues to operate normally in the event of an open wire anywhere in the multiplex circuit.

Ring Topology



Ring Topology

Two open connections in a ring network isolates part of the multiplex circuit and sets a DTC.

Communication lines (bus)

When one ECU sends data to another, the receiving ECU typically sends back a message that it received the data. When a ring network experiences two open wires in the ring, one or more of the ECUs in the network become isolated from the others. An isolated ECU does not receive messages and cannot acknowledge them. The lack of response from an ECU may cause a diagnostic trouble code (DTC) to be set.By studying the network topology and identifying the location of the unresponsive ECUs, you can determine which legs of the circuit contain the open wires.

Two Opens in a Ring Network



Star Topology

A single open in a star network isolates only one component.

Master ECU

In a star network, the master ECU has a separate communication line to each of the other ECUs. An open in any connection affects only one ECU and does not affect the entire network.

Open in a Star Network



Bus Topology

The effect of an open in a bus network depends on the location.

An open on the main bus line isolates part of the network.

An open on a sub bus (branch line) isolates only the component on that branch.

In a bus network, each ECU is connected to a common communication line called the main bus. An open in the main bus divides the network into two segments. The ECUs that are still connected together in one segment can communicate among themselves but cannot communicate with ECUs in the other segment.The connection between an ECU and the main bus is called a sub bus (or branch line). An open in the sub bus isolates only the ECU on that branch.

Open in a Bus Network



Single Wire vs. Twisted Pair

Communication Wire Feature

Twisted-pair Wire This communication line is a pair of twisted wires.Communication occurs by applying Hi or positive (+) and Lo or negative (-) voltages to the two lines in order to send a signal (Differential Voltage Drive).

AV Single Wire This communication wire is thin and lightweight compared with the Twisted-pair Wire.Voltage is applied to this line in order to drive the communication (Single Wire Voltage Drive).

for BEAN, LIN, etc.

Differential Voltage Drive Single Wire Voltage Drive

ECU

Hi

Lo

ECU ECU ECU

Hi

Lo

Communication over a multiplex line consists of a series of voltage pulsesthat form a pattern of bits interpreted as data by the receiving ECU. In a typical multiplex system, the voltage pulses are carried over a single wire.In some multiplex systems (CAN and AVC-LAN for example), a pair of twisted wires carry matching pulses—one positive and one negative. This method reduces electromagnetic interference or noise and is more reliable in circuits requiring a greater degree of transmission reliability.For additional reliability and protection from voltage being induced by nearby wiring, some systems use twisted-pair wires with added shielding (AVC-LAN, for example).

Single Wire vs. Twisted-Pair



Advantage of Twisted-Pair Wiring


3.5 V

2.5 V

1.5 V

0 1 0 1Data

Noise

Single Wire Voltage Drive

4.0 V

0 V

1 00 1Data

1 0

Noise

0 ?

Abnormality

Cancel Each Other

0 10 1

Electromagnetic interference from nearby wiring can induce unexpected voltage spikes (noise) in a multiplex communication line which alters the coded data being transmitted. The receiving ECU has a way of detecting the data has been altered, but it then has to send a request to the sending ECU to retransmit the data. This slows down communication between the ECUs.To keep high-speed networks operating at high speed, twisted-pair wires provide protection from induced noise. When a network that is wired with twisted pair wiring experiences noise, the abnormality affects each wire in the same way, so the effect of the interference is cancelled out.

Advantage of Twisted-Pair Wiring






• Types of Waveforms• Amplitude• Frequency• Pulse Width • Duty Cycle

Section 3 Topics

Signals & Waveforms



Types of Waveforms

Voltage

Time

Voltage

TimeVoltage

TimeVoltage

Time

Voltage

TimeVoltage

Time

Sine WaveSquare

Wave

Rectangular Wave

Pulse Wave

Triangular Wave

Complex Wave

Digital Analog

“Signaling” between circuits and ECUs relies on changes in voltage.When changing voltage is displayed over time, the result is called a “waveform.”

Examples

Electronic and computerized components communicate with each other using electrical signals. Signals can be as simple as the presence or absence of voltage or current on a wire (ON/OFF signal). Signals can also be as complex as a series of 64 voltage pulses (bits) in a data packet containing precise instructions for a receiving ECU to execute.In all cases, it is changing voltage that contains the information for controlling electronic components. When changing voltage is displayed on a graph of voltage versus time, the resulting pattern is called a waveform.

Electronic circuits produce many different common waveforms. Voltage smoothly changing between a low and a high value produces a sine wave. It is often a change in the signal’s amplitude or frequency that conveys information. A square wave is a digital version of a sine wave. (Digital circuits typically just turn voltage on or off instead of smoothly changing voltage the way analog circuits do.)When the amount of time the voltage is high is different from the time the voltage is low, a rectangular wave results. In this type of signal, it can be the ratio between the two times that controls the component.When voltage changes momentarily and then returns to a steady state again, the result is a single pulse, or a pulse wave. Both square and rectangular waves can be viewed as a repeating sequence of voltage pulses. Any sequence of pulses may be referred to as a pulse train.Audio and video signals appear as randomly changing voltage. Data packets flowing between ECUs also appear as random signals. These types of signals produce complex waves.

Electronic Communication

Types of Waveforms



Amplitude

Amplitude: The difference in voltage between two points on a wave.

Note: Voltage scales can vary.

Voltage

Time

Voltage

Time

14 v

-14 v

0 v Peak-to-Peak Amplitude = 28 v

14 v

0 v

7 v Peak-to-Peak Amplitude = 14 v

Sine Wave

Square Wave

Signaling between electronic components is determined by the characteristics of waveforms and the ways in which they change. Therefore it’s important to understand the different types of waveform measurements.

Looking at a graph of a waveform, amplitude is simply the difference in height (voltage) between two points on the graph. Two points often compared are the highest and lowest points. This is peak-to-peak amplitude. Many electronic circuits have a normal operating range. In a circuit with a normal operating range of 0 to 5 volts, for example, waveforms will normally have an amplitude of no more than 5 volts above zero. A signal on such a circuit having a 12-volt positive amplitude could indicate a short to another circuit.

Waveform Measurements

Amplitude



Frequency

Frequency: Number of times a repeating waveform cycles per unit of time.

Note: Time scales can vary.

Cycle = 10 millisecond (ms)

Frequency = 1 / .010 second

= 100 times per second(100 hertz or 100 Hz)

Cycle = 0.5 second

Frequency = 1 / 0.5 second

= 2 times per second(2 hertz or 2 Hz)

Voltage

Time1 cycle

Voltage

Time1 cycle

When a waveform has a recurring pattern, the pattern repeats a certain number of times per second. The number of times it repeats in a second is its frequency in hertz. •One hertz (Hz) equals one cycle per second. •One megahertz (MHz) equals one million cycles per second.In some applications, it is the frequency of a signal that contains the information. A wheel speed sensor is an example. A passive wheel speed sensor creates a sine wave as the wheel rotates. As the wheel rotates faster, the sine wave’s frequency increases proportionately.An active wheel speed sensor, on the other hand, creates a square wave. As the wheel turns faster, the square wave’s frequency also increases.In both cases, the ECU uses the signal’s frequency to calculate speed.

Revolutions per minute (RPM) is a type of frequency. 6000 RPM is equivalent to 100 cycles per second (100 Hz).

Frequency

NOTE




Pulse Width

Pulse Width: The time duration of a voltage change before it returns to a normal level.

Voltage

Time

1 ms. pulse

Voltage

Time

3 ms. pulse

Pulse A Pulse B

Because the pulse widths are different, some ECUs would interpret pulse A as having a different meaning than pulse B.

Voltage

Time

Pulses can also be negative.

One component can send a signal to another with a voltage pulse. In this case, it is the duration of the pulse, or pulse width, that conveys information.In late-model vehicles for example, tapping the horn switch quickly sends a voltage pulse over the BEAN network to the Body ECU. • A 13 ms. pulse causes the horn to sound for 106 ms.• A 30 ms. pulse also causes the horn to sound for 106.ms.• A 100 ms. pulse causes the horn to sound for 173 ms.• An 8 ms. pulse does not cause the horn to sound at all.In this example, the ECU sounds the horn for a pre-calculated length of time based on the width of the pulse (duration of the voltage signal) from the horn switch.

Pulse Width


Duty Cycle

Voltage

Time

Voltage

Time

Duty Cycle: The percentage of time that a circuit is ON.

75% 25%

25% 75%

• Ground-side controlled circuits are ON when the voltage is low.

• Power-side controlled circuits are ON when the voltage is high.

10 ms

10 ms

When voltage alternates repeatedly between a high and a low value, the ratio of time the voltage is high compared to the time it is low can be used to control components. The ratio is called the duty cycle.An example is in controlling the brightness of the dashboard illumination. Older vehicles used a variable resistor to increase or decrease voltage to the lamp to make it brighter or dimmer.In electronic circuits, a modulator can turn a circuit on and off hundreds of times per second. If the amount of time the circuit is ON equals the amount of time the circuit is OFF, the lamp is receiving 50% of the power it would receive if the circuit were just left ON. When the ON time equals 50% of the complete cycle, it is referred to as a 50% duty cycle. Similarly, when the ON time equals 75% of the complete cycle, it’s a 75% duty cycle

Duty Cycle



• The Oscilloscope• PC Oscilloscopes • Basic Operation• Oscilloscope Scales• Repeating vs. Changing Patterns• Scope Pattern Comparison • Trigger Function• Advanced DVOM Features• WORKSHEET: DVOM Advanced Features

Section 4 Topics

Measuring Signals



The Oscilloscope

The oscilloscope displays voltage in graphical form, indicating how the voltage changes over time.

Time

Vol

tage

• The vertical axis represents voltage.• The horizontal axis represents time.

Vol

tage

An oscilloscope’s basic function is to display a rapidly changing voltage signal as a graph over time. Oscilloscopes have long been used to analyze engine ignition and fuel systems where signal frequencies are related to engine RPM. With the introduction of automotive ECUs and multiplex circuits,oscilloscopes have now become important tools in diagnosing bodyelectrical systems as well.

The Oscilloscope




PC OscilloscopesOriginally, oscilloscopes were standalone measuring devices.

In recent years, oscilloscopes have been created for use on PCs or laptop computers.

Required test leads or cables are not shown for either scope.

Until recently, oscilloscopes have been standalone measuring devices with some type of display to show the changing voltage pattern. Newer oscilloscopes don’t have their own display, but instead connect to a personal computer (PC) or a laptop computer where they can use the computer screen to display the waveforms.

PC Oscilloscopes


An oscilloscope has test leads similar to a DVOM. The leads are connected in a circuit where you want to measure a signal. When operating, the scope draws a line, or trace, across the display screen corresponding to the voltage it is reading. As voltage increases or decreases, the line moves up and down the screen as it is traced.To keep the line from going off the top or bottom of the display screen, a vertical control adjusts the voltage scale so the trace stays on-screen.A similar control adjusts the time scale.

Basic Operation

Basic Operation

• The scope repeatedly draws atrace across the screen from left to right.

• The trace moves up or down as circuit voltage changes.

Vol

tage

Time

When the test leads are connected to the circuit:

A vertical controldetermines the voltage scale.

A timebase controldetermines how fast the trace is drawn and the time scale.




Oscilloscope Scales

Signal voltage and frequency can vary widely.• To properly view a signal, the voltage and time scales must be set appropriately.

Volts per Division

5 V/Div

10 ms/DivTime per Division

1 ms/Div

5 V/Div

5 ms

Same square wave, poor time scale

12 V

10 ms

Square wave

An oscilloscope screen is divided by horizontal and vertical lines called divisions. When setting the display screen’s voltage scale, you specify how many volts you want each division to represent.In the example above, the signal voltage changes by 12 volts from low to high. The voltage scale in the screen in the illustration has only five divisions. To keep the signal trace from disappearing off the top of the screen, the technician has set this voltage scale to 5 volts per division (5 V/DIV). Other settings are possible (6 V/DIV, for example) that can also keep the entire signal visible. Sometimes it requires a little experimentation to see which scale makes the signal easiest to evaluate.Setting the time scale appropriately is also important for being able to see a signal. In the first example above, the time scale has been set to 10 milliseconds per division (10 ms/DIV). This scale makes the signal’s 20 ms cycle very apparent. In the second example, a time scale of 1 ms/DIV zooms too far in so that only a tiny, unchanging snippet of the signal is visible.Once again, other appropriate time scale settings are possible (20 ms/DIV, for example) that can also display the signal characteristics clearly. If settings aren’t specified for the signal you're monitoring, it may take some experimentation to find the best time scale setting.

Oscilloscope Scales


Oscilloscope Scales

The Repair Manual provides the appropriate scales for specific signals.

2007 Tundra

Compressor Lock Signal

CANH Communication Signal

Terminal No. (Symbols)

Tool Setting Condition

J19-11 (CANH) -J19-14 (GND)

1 V/DIV, 10 μsec/DIV

Ignition switch ON

Terminal No. (Symbols)

Tool Setting Condition

J19-8 (LOCK) –J19-14 (GND)

200 mV/DIV, 10 ms/DIV

Engine is runningBlower switch LOA/C switch ON

When following troubleshooting procedures in the Repair Manual, specific settings for the voltage and time scales are often provided to eliminate the need to experiment. It's best to use these provided settings for comparing the signals you observe on your scope display to those illustrated in the “Terminals of ECU” section of the Repair Manual.

Repair Manual Suggested Scales




Repeating vs. Changing Patterns

If the pattern is not repeating, the trace appears noisy at any scale.

The voltage does not follow a pattern.

Start 100 ms

101 ms 200 ms

201 ms 300 ms20 ms/Div

100 ms

As each new trace is drawn on the same screen, the pattern appears “noisy.”Trace 1

Trace 2

Trace 3

When a voltage signal is changing rapidly, the oscilloscope trace has to redraw itself on the screen many times per second. In the example illustrated above, the time scale is set to 20 ms/DIV so the entire display represents 100 ms or 1/10 of a second. Therefore, the screen display will be retraced 10 times per second.The signal this scope is measuring, however, is not the type that has a repeating pattern. Looking at the first three 100 ms traces shown on the left, each trace is different. When those traces are drawn on the sameoscilloscope screen all within 3/10 of a second, it’s impossible to see any pattern in the overlapping traces. The result is what appears to be a “noisy”signal. This type of signal pattern is common in audio systems.

Repeating vs. Changing Patterns


Capturing Waveforms

You can examine a non-repeating waveform by capturing it.

300 ms of signal captured in scope memory

100 ms view

Start200 ms

300 ms

Scroll to view

101 ms

If it’s necessary to see exactly what’s happening in a signal that is not repeating, many oscilloscopes offer a capture feature. When a waveform is captured, a designated time period of signal is recorded in memory so it can be played back and examined in detail.The specifics of how this feature operates vary with different model oscilloscopes. In general, however, the more memory available for recording, the longer the time period that can be captured and the greater quantity of captures that can be kept in memory at one time.Two of the advantages of PC oscilloscopes are a large memory andremovable storage media for saving captures.

Capturing Waveforms




Scope Pattern Comparison

These patterns were captured 3 seconds apart.

Signals are not identical, but they are good signals.

Trace 2Trace 1 CAN Network Signal (Low)

Hint: If in doubt, compare pattern to a known good vehicle.

How do the traces above compare to what is shown in the Repair Manual?

Multiplex communication signals are prime examples of signals that do not have a repeating pattern. The timing and width of the voltage pulses vary depending on the content of the messages the ECUs are trying to send over the network. Compare the signal to a conversation between people. In natural speech, you wouldn’t expect to see the same sentence repeated at a regular frequency.For that reason, when comparing scope patterns to specifications in the Repair Manual, the comparisons are not likely to be exactly the same. In the case of the CAN low signal, the key observation is that the voltage varies between 1.5V and 2.5V and that the pulses indicating active communication are visible.

Scope Pattern Comparison


The Effect of Scale

These are traces of the same signal.

10 μsec/DIV 50 μsec/DIV

Why do these traces look so different?

Repair Manual

0.5 V/DIV

0.3 V/DIV

Trace 2Trace 1 CAN Network Signal (Low)

When examining or comparing scope patterns, be aware of how small differences in scale can completely alter the signal appearance.

NOTES:




0 v

1 v

2 v

-1 v

Trigger Function

A trigger function synchronizes the traces for a stable pattern.

• When the trace reaches the right edge of the screen, it has to return to the left side to start another sweep.

• To synchronize the traces, the trigger delays the next sweep until the trigger event occurs.

The trace ends with voltage going negative

• If the next sweep starts immediately, it won’t synch with the signal already on the screen.

• The display will drift or appear noisy.

This trigger is set to restart the sweep when voltage crosses 1V going positive.

All scopes have a trigger function which is necessary for stabilizing the scope pattern.

NOTES:


Other Trigger Uses

The trigger function can also delay capturing a waveform until:

A signal appears

An intermittent fault occurs

Begin capturing when voltage goes over 0.1 volt.

Begin capturing when voltage goes over 2v.

A trigger can also be set for capturing a waveform when a specified condition occurs.

NOTES:




Advanced DVOM Features

MIN/MAX Recording Mode

Relative Delta

Press

to begin recording

Press

to pause recording

current reading as a reference value and zeroes the display

Stores the

1

2

4

Press 3and hold to toggle between 100ms and 1ms sampling speeds

1 2

3 4

Some types of electrical measurements that are commonly made using an oscilloscope can be made using the advanced features of many DVOMs. The following are features of the Fluke 87.

When voltage is varying, sometimes the only measurements needed are the upper and lower voltage readings. On a CANL communication line, for example, communication signals create voltages between 1.5V and 2.5V. With the MIN/MAX Recording feature, the DVOM records and displays the minimum and maximum voltages to verify the voltage range.MIN/MAX is also helpful for identifying transient voltage spikes. If a momentary 12V spike were to appear on the CANL communication line, the 12V MAX reading would indicate a problem.

Set the voltage range before selecting MIN/MAX. If auto-ranging sets the initial range too low, the MAX readings will be O.L.

By pressing the Peak MIN/MAX button (also called the “alert” button), you can toggle the sampling speed between 100 milliseconds and 1 millisecond. Any voltage signal lasting at least as long as the sampling speed is recorded.

The Relative Delta function allows you to select a reference value, and then displays the difference between the current reading and the reference value. This might be useful when looking for variations in voltage from a reference value. In bench testing for resistance, touching the leads together and selecting Relative Delta effectively deducts the resistance of the leads from component resistance measurements.


MIN/MAX Recording

Peak MIN/MAX

Relative Delta

NOTE


- 074.9 1 cycle


Frequency and Duty Cycle

Press

to measure frequencyonce

Press

to measure duty cycleagain

1

2 Press

to toggle between positive and negative trigger for duty cycle

Positive Trigger

Negative Trigger

75% duty cycle

1 cycle

25% duty cycle

3 Changes between + and – to indicate trigger direction

% 3

12

If you only need to determine a signal’s frequency, you could use the frequency measuring feature available with an advanced DVOM. It measures frequency by counting how many times per second a varying voltage or current reading crosses a selected threshold.

Similarly, some DVOMs can calculate duty cycle by measuring the percentage of time a signal is above or below a selected threshold during one cycle. The result is displayed as a percentage.The percent duty cycle reading assumes the first part of the cycle is the ON portion. The value will be different depending on whether the cycle is interpreted as starting with a positive-going (rising) or negative-going (falling) voltage. In a ground-side controlled circuit, the load is ON when the voltage is low.Therefore you want to set the cycle to start when the voltage falls so the percentage of ON time is measured properly. This requires setting the DVOM for a negative trigger. While measuring duty cycle on the Fluke 87, you can toggle between positive trigger and negative trigger by pressing the Peak MIN/MAX button.

Frequency Measurement

Duty Cycle



Worksheet

DVOM Set-up & Advanced FeaturesClassroom Worksheet:

In this worksheet you will use a DVOM and a signal generator to measure signals for voltage, frequency and duty cycle.

Use this space to write down any questions you may have for your instructor.

NOTES:



Demonstration

Instructor DemoUsing DVOM Resistance SettingThe instructor will demonstrate using a resistance measurement to measure frequency and duty cycle in the SI circuit of a blower motor.

M

B+

Blower Motor

SI

Varying duty cycle (voltage) regulates motor speed

AC Amplifier

Steering Pad Switches

IC*

*The integrated circuit (IC) not only drops the voltage for the SI circuit, it also protects the motor from a short in the SI circuit.


NOTES:



• Introduction• Auto Features• Voltage and Time Scale Settings

• Turning the Trigger On• Setting the Trigger• Start and Stop Capturing• Horizontal Zoom• Rulers

Section 5 Topics

Using a PicoScope™ • Sample Rate

• Displaying Two Channels• Separating the A-B Traces• WORKSHEET: PicoScopeBasic Setup

• WORKSHEET: Using DVOM & PicoScope

• DEMO: PicoScope & Power Window Circuit



Introduction to PicoScope™

• Oscilloscope software on a PC

• Hardware connected to PC via USB cable

• 1-channel, 2-channel and 4-channel models

PicoScope™ is a brand of PC-based oscilloscope. The PicoScopehardware connects to a personal computer via a USB cable and requires PicoScope software on the PC to display the scope signals. It is available in 1-channel, 2-channel and 4-channel models.

Each channel has a lead wire that can be connected to a circuit to be monitored. Various lead connectors are provided for convenientlyconnecting3 to pins, wires or terminals. The accessory kit also includes inductive clamps for measuring current flow in wiring without disconnecting the circuits.When the leads and hardware are all connected, the PicoScope software running on the PC controls all of the PicoScope’s measurement and display functions.

Introduction to PicoScope™

Connecting the Leads




Auto Features

In Auto mode, the scope selects a voltage range that best matches the signal’s peak-to-peak voltage.

The Auto Setup button allows the scope to select both the voltage and time scale.

As with most software programs, the PicoScope software has a great variety of features. This section introduces the features you will use most frequently. To learn about additional features, refer to the PicoScope manual included in the kit. It can also be referenced within the software program by clicking on Help.

Because the frequency and amplitude of different signals vary widely, there is not a single setting of voltage and time scale that will display all signals well. One of the challenges in using a traditional oscilloscope is dialing in the signal, which involves trying different voltage and time scale settings until the signal is displayed clearly. To dial in a signal more quickly, the Auto feature automatically selects the voltage scale that best displays the signal's peak-to-peak voltage. This provides a waveform that is completely captured within the display, and allows the setting to be fine tuned if necessary.

The Auto voltage scale feature does not try to set an optimum time scale. You will likely need to adjust the time scale to properly display the signal.

The lightning bolt icon selects Auto Setup which not only selects the voltage scale, but also the time scale. These automatic settings usually bring a signal into view, but are often not the best scales for observing it.

PicoScope Features

Auto Voltage Scale

NOTE

Auto Setup


Voltage & Time Scale Settings

Drop-down menus display the available settings for the voltage and time scales.

Voltage choices define the range of the entire screen.

Time choices define seconds per division. The screen has 10 divisions.

To compare signals to those shown in the Repair Manual, you mustmanually set the voltage scale.In the Repair Manual, the suggested voltage scale settings are expressed as volts per division. The drop-down menu for selecting the voltage scale on the PicoScope, however, offers choices that define the range of the entire screen. Therefore it’s necessary to make a simple conversion.If the Repair Manual suggests 2 V/Div and the PicoScope screen has 10 divisions, then the desired voltage range is 2 x10 = 20V. A +10V scale would provide a range of 20 volts from -10V to +10v. If the signal actually fluctuates between 0V and 12V, however, part of the waveform will be going off the screen. In such a case, make an adjustment to the voltage scale setting as needed to display the entire signal (+20V).

The PicoScope does not have an auto time setting, so you will have to manually select the appropriate scale. The drop-down menu in this case does give choices in seconds per division, so no conversion is necessary when using Repair Manual recommendations.If you don’t have a recommended time scale and the signal is unfamiliar, look at the waveform at a very high setting and a very low setting. Seeing the signal from both extremes helps you determine the appropriate scale.

Manual Voltage Scale Settings

Manual Time Scale Settings




Turning the Trigger ON

Setting the trigger properly can stabilize a signal pattern, or set the scope to capture a signal only when it goes in or out of a specified range.

If a pattern is sliding left and right or moving too fast to be seen, setting the trigger can stabilize the waveform. With the trigger on, the signal is not traced on the screen until a specified trigger event occurs.The trigger mode can be set to:Auto – The scope waits for a trigger event before capturing data. If there is no trigger event within a specified time, it captures data anyway. It repeats this process until you click the Stop button. Auto mode does not set the trigger threshold automatically; you must do this manually.Repeat: The scope waits indefinitely for a trigger event before displaying data. Then it waits for another trigger event, and displays the data. It repeats this process until you click the Stop button . If there is no trigger event, it displays nothing. Single: The scope waits once for a trigger event, then stops sampling. To make it repeat this process, click the green START button.The trigger can also be very useful in capturing spikes or other unusual circuit activity. To capture an intermittent fault, set the trigger to start capturing only when the voltage goes out of range.

Turning the Trigger On


Setting the Trigger

A

B

C

D F

E

A. Advanced Triggers – Access a selection of advanced triggers on certain scope devices.

B. Trigger Channel - Selects a channel as a source for the trigger.

C. Rising Edge – Trigger when a signal crosses the threshold in the rising direction.

D. Falling Edge - Trigger when a signal crosses the threshold in the falling direction.

E. Threshold – The voltage level that the signal must cross to trigger a capture.

F. Pre-Trigger – The amount of data captured before the trigger event (as a percentage of the total capture time).

When the trigger event occurs, the scope begins displaying the signal. The three most important trigger settings are:Threshold – Capture begins when the signal reaches this voltage. Not having this threshold set appropriately is the easiest way to get unsatisfactory trigger results. It must always be set manually.Rising or Falling Edge – This selection specifies whether capture starts when the voltage signal crosses the threshold voltage while rising or while falling.Trigger Channel – When measuring two or more signals simultaneously, you must specify which channel to watch for the trigger event.

Setting the Trigger




Start and Stop Capturing

While capturing, the display changes as the signal changes.When stopped, the last capture is frozen.

Start or resume capturing

Stop capturing

When you have a lead connected and start the PicoScope software, the screen displays a constantly updated real-time voltage reading. If the voltage is changing rapidly, you will see a rapidly changing waveform.Depending on the signal, you may be able to obtain the information you need from examining the moving waveform. For example, on a CANH bus line, you’re principally looking for a signal that fluctuates rapidly between 2.5V and 3.5V.In some cases, however, you may need to freeze the signal so you can look at the wave pattern more closely. To freeze the signal, click on the red STOP icon in the lower left corner.To resume capturing, click on the green START icon.

Pressing the spacebar on the keyboard also stops and starts capturing.

Start and Stop Capturing

NOTE


Horizontal Zoom

Horizontal zoom magnifies the graph in the horizontal direction.

1x zoom

The screen can be scrolled left and right to locate and examine locations of interest.

8x zoom

Notice the very compact waveform in the upper-right screen above. The time scale setting in that example captured a large number of cycles. The long time setting and large number of cycles were necessary in that case to clearly show the recurring glitches in the signal.To more closely examine these abnormalities in the signal, expand the waveform using the horizontal zoom function. Depending on the point at which the waveform is expanded, however, the abnormality may not be visible. To see it, a scroll bar at the bottom of the screen (not shown above) allows you to scroll left and right to view any part of the captured signal.To return to the original view, reset the scale to x1.

Horizontal Zoom




Rulers – Measuring Cycle Duration

Drag the white box to the right to move the rulers onto the screen.

510 ms 694 ms 184 ms

Calculates the time between the rulers.

Rulers

20 Hz1/Δ5.43 Hz5.43 Hz1/Δ

Calculates frequency

The software provides rulers to make obtaining accurate time and voltage measurements easier.Vertical Rulers (Time) – To place a vertical ruler at any point on the screen, click and drag the small white box in the lower left corner. Two rulers are available. The ruler measurements and difference between them appear in a box at the top of the screen. A typical use for vertical rulers is to measure the duration of one cycle. The duration of a cycle can be converted into frequency by dividing the duration (must be in seconds) into 1. Example:

1= 5.4 hertz (cycles per sec.)

.184 sec./cycle

Whenever the vertical rulers are used, the PicoScope automatically performs the frequency calculation and displays the result in the lower right corner of the screen.

Rulers


Rulers – Measuring Peak-to-Peak Voltage

Drag the blue box down to move the rulers onto the screen.

Rulers

Calculates the voltage between the rulers.

Horizontal Rulers (Voltage) – To place a horizontal ruler at any point on the screen, click and drag the small blue box in the lower left corner. Two rulers are available. The ruler measurements and difference between them appear in a box at the top of the screen.Horizontal rulers are typically used for measuring a signal’s peak-to-peak voltage.

Rulers (Cont’d)




Sample Rate

The scope attempts to capture the number of samples per second specified here.

Use the up/down arrows to change the setting.

Settings range from 50 per second (50 S) to 200,000,000 samples per second (200 MS). The actual number of samples could be different.

To display a voltage signal that is rapidly changing, the oscilloscope must take sample voltage measurements very frequently. If samples are not taken rapidly enough, the displayed signal will not accurately represent the actual signal pattern.In most cases, a fairly high sample rate displays the signal in detail. In some cases, however, too much detail makes unimportant noise in the signal visible. Reducing the sample rate may filter out the unwanted detail so the fundamental wave pattern is clearer..

Sample Rate


Displaying Two Channels

To turn on the B channel, select a voltage range from the pull down menu.

B-Channel voltage scale

B-Channel trace

B-Channel ruler

Viewing two signals at the same time can be very helpful in a variety of diagnostic situations. With a two-channel or four-channel scope, the additional channels are turned on and off using each channel’s voltage scale setting. To distinguish the different signals, they are color-coded.Voltage scales are displayed on both the left and right sides of the screen. You can set different voltage scales for each signal, but the time scale is the same for all signals.

Displaying Two Channels




Separating the A-B Traces

To separate the traces:

Or click here for this dialog box

Click and drag the voltage scale upward

Click and drag the voltage scale downward

In many cases, overlapping signals can make it difficult to analyze the waveforms. Separating the waveforms is as simple as clicking on the voltage scale and dragging it up or down to reposition the signal on the screen.Another way to offset the traces is to click on the colored box in the lower left or right corner. This brings up a dialog box that allows adjustments to scale and offset. To return to the default setting, click on the button with the “return” arrow on it.

Separating the A-B Traces


Printing, Saving and Sending Patterns

Use the File menu to print or save the current waveform.

Once a file is saved, it can be transmitted electronically the same as any other file.

If your diagnostic efforts require you to print a waveform, use the File menu in the upper left corner to access the printer functions. Use the same File menu if it’s necessary to save a captured pattern. Make note of the folder where the saved file is stored so that you can retrieve it later when needed.Sending a saved waveform file is the same as sending any other file. Note that if the recipient does not have PicoScope software, be sure to save the waveform in a format they will be able to open.

Printing, Saving and Sending Patterns



Worksheet (1 of 2)

In-class PicoScope: Basic Set-upClassroom Worksheet:

In this worksheet, you will set up the PicoScope to measure signals from a signal generator and practice using the PicoScope features to display signal patterns.


NOTES:



Worksheet (2 of 2)

Using DVOM & PicoScopeShop Worksheet:In this worksheet you will:• Locate and back probe a dimmer-controlled interior lamp or LED• Practice measuring Voltage (V), Hertz (Hz), percentage values (%) using a DVOM• Use the PicoScope to display the signal pattern.

Instructor DemoPicoScope & Power Window Circuit

The instructor will demonstrate measuring and displaying signals using the PLS1 and PLS2 signals of a Power Window System.


NOTES:



• Inductive Clamp• Preparation for Use• Converting Measurements to Amps• Amp Clamp Applications• WORKSHEET: Inductive Clamp I -Measurement & Conversion

• WORKSHEET: Inductive Clamp II - Monitor A/C Blower Motor

Section 6 Topics

Using an Inductive Clamp



Inductive Clamp

An inductive clamp measures current flow without opening the circuit.

Current flowing in a wire creates a magnetic field around the wire.

Wire

Current flow

Magnetic field

An inductive clamp placed around the wire measures the strength of the magnetic field to determine current flow.

Right hand rule determines the direction of the magnetic field.

An inductive clamp is an accessory that can be used with a DVOM or oscilloscope to measure current. It may also be called an amp clamp or a current clamp.The inductive clamp operates on the principles of magnetism and induction. Electrons flowing in a wire generate a magnetic field around the wire. If another wire or conductor is placed in the magnetic field, the magnetic force causes electrons in the second wire to flow. This is called electromagnetic induction. The strength of current flow and the strength of the magnetic field are directly proportional.The inductive clamp takes advantage of this principle by placing a probe around a wire where it can measure the strength of the magnetic field and thus determine the current flow.

The direction of the induced magnetic field depends on the direction of current flow through the wire. If you were to wrap your right hand around the wire with your thumb pointing in the direction of current flow, your fingers would then circle the wire in the direction of the magnetic field. This is called the right hand rule.Because the magnetic field has a polarity, it’s possible to obtain negative readings if the clamp is placed on the wire backward. If this occurs, simply reclamp the wire with the clamp flipped over.

The Inductive Clamp

Polarity



High Current and Low Current Clamps

Use a high current inductive clampon large wires and circuits with high current flow.

For smaller wires and lower current circuits, use the low current inductive clamp.

Note: Each inductive clamp is rated according to its maximum current measuring capability.

Each inductive clamp is rated according to its current measuring capability. Ratings can vary from 10 amps to 2000 amps.As a safety feature, low current clamps often have jaws that do not accommodate very large gauge wiring. A typical low current clamp is rated between 10 and 60 amps.High current clamps have larger jaws for larger gauge wires. A typical high current clamp is rated between 100 and 600 amps. Very high current clamps may be rated between 1000 and 2000 amps. In general, the higher the current rating is, the less precise the measurements are.

Current Rating



Preparation for Use

After each use, capacitance in the clamp can store a charge that will make the next reading inaccurate.

To dissipate the stored charge, press to open the jaws and let them snap shut several times.

Then zero the tool to cancel the effect of any residual magnetic field.

Clamp (jaws)

Though there are a wide variety of inductive clamps for DVOMs and oscilloscopes, their basic operation is similar for almost all models. The clamp has a a set of jaws that can be opened and placed around a wire to be measured. After each use, capacitance in the clamp can store a charge that will make the next reading inaccurate. To dissipate the stored charge, open the jaws and let them snap shut several times. Next, press the zero button on the clamp to calibrate the reading and cancel the effect of any residual magnetic field.

The inductive clamp has an internal battery. Turn the clamp OFF when not in use to keep the battery from discharging completely.

Preparation for Use

NOTE



Converting Measurements to Amps

The sensitivity switch on the clamp specifies what conversion factor to use.

When an inductive clamp is used with a DVOM, the meter must be set to measure voltage

Convert the voltage reading to amps using a conversion factor.

10mV / 1A100mV / 1A

OFF

At 100mV / 1A, the 45mV reading equals 45/100 = 0.45A

45mV

(e.g. slide switch)

Note: Not all clamps have a sensitivity switch, but all clamps have a conversion factor.

An inductive clamp actually measures magnetic field strength, not current flow. Therefore when an inductive clamp is used with a DVOM, the meter is set to measure voltage.Most amp clamps have a switch to set the clamp for high or low sensitivity appropriate to the current being measured. The switch is labeled with a millivolts-to-amps ratio needed to convert the DVOM millivolts reading into amps.Different clamps may express conversion factors differently:•10mV / 1A and 100mV / 1A are based on common units of 1 amp.•1mV / 100mA and 1mV / 10mA are based on common units of 1mV.When expressed in common units of 1 amp, the conversion formula is:

mV measuredA =

100mV (or 10mV, depending on scale)

When expressed in common units of 1 mV, the conversion formula is:mA = mV measured X 100 mA

(or 10 mA, depending on scale)

Converting Measurements to Amps



Amp Clamp Applications

Locating short circuits and finding parasitic draws:

When current is found, narrow it down to one wire.

Clamp a group of wires at a time.

85mV

85mV

One of the disadvantages of the amp clamp is that current measurements are not very precise. Precision varies with the quality of clamp. Readings may be 20% to 50% off from actual when measuring current below 100 milliamps.The great advantage of an amp clamp, however, is that you don’t have to open the circuit to measure current. This is exceptionally helpful in diagnosing short circuits and parasitic draws where the precise current value is not important.The problem with opening circuits while diagnosing shorts and parasitic draw is that power interruptions can launch startup cycles for a variety of ECUs. It can be some time before these ECUs quiet down. Until then, current may be flowing temporarily in many circuits and masking the problem circuit.Another problem with opening circuits is that cycling power may reset a component that was drawing current and may temporarily “fix” the problem.

When diagnosing a short circuit or parasitic draw, the first objective is identifying the circuit with unexpected current flow. Then your objective is tracing current flow through the wiring until the current flow stops or you find the failed component.• After determining the most likely place to begin, start by clamping a harness or groups of wires to detect which has current flow.• If current is found in the harness or group, test each wire individually to find the active wire.• Use the EWD to follow the wire through junction blocks and connectors to find the problem source.


Diagnosing Short Circuits and Parasitic

Draw




Vehicle being diagnosed:

Diagnosing intermittent motor failures using an oscilloscope:

Known good vehicle:

Starter Motor Current

The PicoScope and many other oscilloscopes have amp clamps available as optional equipment. One of the applications of an amp clamp and oscilloscope is in diagnosing motor faults. One of the problems with motors on the verge of failure is they exhibit intermittent faults. Resistance in windings or contacts may fluctuate for an extended period before degrading to the point of complete failure. These fluctuations are not revealed in typical DVOM readings. An oscilloscope’s high speed measurements, however, can detect fluctuations in current caused by internal variations in motor resistance. Comparing the current signal pattern to a known good vehicle can reveal if a motor is starting to fail.

With many oscilloscopes, using an amp clamp does not require converting millivolts to amps. The oscilloscope can be set to apply the correct conversion factor and display the result in amps.

Diagnosing Motor Faults with an Oscilloscope

NOTE



Worksheets

Inductive Current Clamp I: Measurement & Conversion Classroom Worksheet:

Some Inductive Current Clamps use a conversion factor for sensitivity. In this worksheet you will practice using the conversion factor to convert voltage to an amperage value.

Shop Worksheet:

In this worksheet you will monitor the A/C Blower Motor amperage using a DVOM equipped with an Inductive Current Clamp.

Inductive Current Clamp II: A/C Blower Motor


NOTES:



• Additional Properties of MPX Protocols

• BEAN Networks• LIN Networks• CAN Networks• AVC-LAN Networks • Gateway ECUs• Transmit/Receive Charts• BEAN Diagnosis• WORKSHEET: BEAN Network Diagnosis

• DEMO: Diagnosing a BEAN Circuit

Section 7 Topics

Multiplex Circuit Diagnosis

Hi LODLC 3

ECU ECU ECU

• LIN Diagnosis• WORKSHEET: AC LIN Interface

• CAN Diagnosis • WORKSHEETS: CAN Network Diagnosis (3)

• AVC-LAN Diagnosis• WORKSHEET: AVC-LAN Inspection

• Other MPX Circuits• WORKSHEET: A/C Bus Servo Motor Operation



Additional Properties of MPX Protocols

Protocol: A set of rules and standards for communication between networkedcomponents. Protocols establish the standards for a variety of possible network properties.

Properties: ConventionsCommunication Direction: One-way, two-way

Transmission Timing: Periodic, event-drivenCollision Detection & Recovery: Retransmission delay, priority scheme

Data Casting: Broadcast, unicast, multicastSleep Mode & Wake-up Function: Available, not available

The network protocols in Toyota vehicles include:• BEAN• CAN• LIN• AVC-LANEach protocol defines the rules and standards necessary for components on the network to communicate with one another. Their rules and standards describe various network properties and their conventions. This section discusses some of these properties and typical conventions in more detail.

Additional Properties of MPX

Protocols




Engine ECUEngine ECU

Communication Direction

One-way communication(mainly used for Door Bus)

Two-way communication

Data

One-way or two-way

Power Window Master Switch

Main BodyMain BodyECUECU

Transmitter Receiver

Switch Signal (e.g. P/W Open)

• Water Temp• Ambient Temp.

AC Compressor ON

Receiver

TransmitterA/C ECUA/C ECU

Receiver

Transmitter

Data

Data

Communication direction is one of the considerations in multiplex network design. Toyota networks may communicate in either a one-way direction or a two way direction.The directional design provides for two different situations:In one-way communication, one component transmits data to another and waits for an acknowledgement. In the example above, the Power Window ECU transmits data to the Main Body ECU that the power window switch is open. The Main Body ECU only acknowledges receipt of the transmitted data.Two-way data transmission involves data flowing in both directions – not just data and acknowledgement, but actual data in both directions. In the example above, the Engine ECU transmits data related to the A/C compressor’s ON status and the A/C ECU acknowledges receipt of that data and replies with additional data related to the water and ambient temperature.BEAN communication direction can be either one-way or two-way. The CAN, LIN, and AVC-LAN are all two-way communication networks.

Communication Direction


Page 86

Transmission Timing Periodic and event-driven Periodic TransmissionData which always needs to be updated is sent to participating ECUs periodically.

Water Temp.

Event TransmissionData is sent to participating ECUs when any of the relevant switches are operated.

OFFON

W W W

If a switch is operated during periodic data transmission, a switch operation signal is inserted between periodic data. Periodic data transmission resumes after event transmission.

WEngine Engine ECUECU

Meter Meter ECUECU

Water Temp. Water Temp. SensorSensor



Engine Engine ECUECU


Meter Meter ECUECU


W

S SSwitch

Operation

WS

W W S W W S W

Another network property taken into consideration in design is the transmission timing of the data. Data may be periodically transmitted or it may be event-driven.Periodic data, such as a water temperature signal or engine speed, is transmitted at regular intervals. Event-driven data is transmitted when an event occurs, such as when a switch is thrown.

Transmission Timing




Collision Detection & Recovery

Retransmission delay or priority scheme

Data Data

When two ECUs attempt to transmit data at the same time, a data collision occurs.

Retransmission delay (BEAN)

Each ECU stops transmitting for a predetermined time interval. ECUs resume transmitting one after the other, with the highest priority ECU going first. (10 kbps)

Priority scheme (CAN)

The ECU with the highest priority message is allowed to continue transmitting. Other ECUs stop until the communication line is no longer busy. (250 to 500 kbps)

ECU ECUECUECU ECU

In a multi-master network (such as BEAN or CAN), collision detection is a method of resolving data collisions that might occur when more than one ECU transmits at the same time. Multiple access to the serial data bus allows individual ECUs to function independently and transmit at any time they sense an idle network. If a data collision occurs, the ECUs in some networks (such as the BEAN) each wait for a slightly different predetermined time interval and then resume data transmission. The sequence in which they restart is based on their priority.CAN uses a message priority method for resolving conflicts on the network. When a data collision occurs, the ECU with the highest priority message continues transmitting while the other ECUs stop. The other ECUs can resume transmitting when they detect the communication line is not busy. By not interrupting transmission of the priority message, the CAN protocol is able to operate at faster speeds.Both LIN and AVC-LAN networks are controlled by a master node, so no collisions can occur and arbitration or collision management in the slave nodes is not required.

Collision Detection


Data Casting

Broadcast CommunicationData is sent from an ECU to participating ECUs.

Unicast CommunicationData is sent from an ECU to a certain ECU.

Multicast CommunicationData is sent from an ECU to a group of other ECUs.

Broadcast, unicast and multicast

ECU ECUECUECU ECU

ECU ECUECUECU

ECU ECUECU

ECU

ECUECU

Transmit

Transmit

Transmit Receive Receive Receive Receive

Receive

ReceiveReceive

Another attribute of network protocol is data casting. There are three basic types of data casting methods used.• Broadcast communication where every node on the network receives the data. • Unicast communication where data is only addressed to one node on the network and the address is ignored by the other nodes.• Multicast communication where data is transmitted from one node on the network and addressed to a group of other nodes.The Body Electronics Area Network can transmit data using all three types of data casting methods.The Controller Area Network transmits using broadcast and multicast methods. Individual ECUs can ignore sent data but will send a receipt of data transmission. A CAN Bus Check is a broadcast signal which checks to confirm which ECUs are responding. Replies are returned in the order of reception.Local Interconnect Network transmits using the multicast method.Audio Visual Communication-Local Area Network uses all three.

Data Casting




Sleep Mode & Wakeup Function

Not all systems have sleep mode. When a system with sleep mode judges that the vehicle is not being used, it stops communication of all ECUs to reduce parasitic current. (BEAN, CAN, LIN)

Available or Unavailable

ECU

ECU ECU

Sleep• IG-OFF• All doors are closed• After a predetermined time the system

goes to sleep.

Wake-upDuring sleep, if any of the relevant switches are operated:• Open the door• Unlock the door, etc.the affected ECU sends a “wake-up”message to other ECUs.

Wake-up signal

zz

zz

What would keep the network from going to sleep?

ECU

ECU ECUzz

In the BEAN and LIN protocols, ECUs periodically transmit data. This activity uses battery voltage and creates a normal parasitic draw. To reduce parasitic draw when the vehicle is not being used, ECUs enter “sleep” mode after a set time when the ignition is off and the doors are closed.After the ignition has been turned OFF, a CAN node may also enter sleep mode to reduce the power consumption. The transmitter portion of the transceiver module is switched OFF, however the receiver part can remain active to check for activity on the bus.

When any network-related switch is operated, the associated ECU “wakes up” and sends a wake up signal to all the other ECUs on the network. In a LIN network, both the master and slaves are able to wake-up the network.AVC-LAN does not have a sleep mode and wake-up function.

• A dead battery from a parasitic draw can be caused by a BEAN, LIN, or CAN network that is not going to sleep. • A network can be kept awake if one of the ECUs on the network is receiving constant input from a faulty switch or sensor.• Circuits operating properly can also keep a network awake - an immobilizer key left in the key cylinder (with ignition off) for example.

Sleep Mode

Wakeup Function

SERVICE TIP


Body Electronics Area Network (BEAN)

Topology: • Daisy chain configuration to improve reliability in the event of open circuit• Single-wire voltage drive (speed = 10 kbps)

2004 Avalon

MPX2

Body ECU

Theft Deterrent ECU

MPX2

MPX1

Power Seat ECU

MPX1

Driver Door ECU

Passenger Door ECU

MPX2

MPX3

MPX4

MPX1

MPX1

MPX1

MPX2

MPX1

Ring

Bus

Bus

The Body Electronics Area Network (BEAN) is a proprietary network developed by Toyota. It is a low-speed protocol typically used for ordinary body electrical systems such as windows, doors, mirrors, seats, etc.The BEAN uses a combination of the ring and bus styles to network its ECUs. This style of connection is also called a daisy chain. The advantage of a ring configuration is that the ECUs in the ring part of the network can continue to communicate even if there is an open in one area because the transmission can travel via two possible pathways. Even in the ring configuration, if the communication line is cut at more than one point, communication becomes impossible. In recent Toyota systems, however, a back-up bus is provided to maintain limited communications. A backup bus usually links the combination switch, front Controller, and Main Body ECU.Several BEAN networks may be connected to each other via a Gateway ECU or to other networks via the GatewayBEAN also provides the capability for customizing certain system settings using Techstream.

Body Electronics Area Network




Local Interconnect Network (LIN)

Master-Slave Protocol: • Master sends request for data to the slave• The slave responds with data requested• Slaves cannot transmit unless requested (except for “wake-up” message)• Slaves cannot communicate with each other

LIN

Master ECU

SlaveECU

SlaveECU

SlaveECU

SlaveECU

Speed = 20 kbps(e.g. Power Window Master Switch, Sliding Roof ECU, etc.)

LIN was developed by a consortium of European car manufacturers as a lower cost alternative to CAN. Though its maximum transmission speed is only 20 kbps, its cost is two to three times lower per node. It is typically used to control sensors and actuators in non-critical systems such as windows, doors, seats and air conditioning systems.

The LIN protocol uses an AV (automotive vinyl) single wire in a star topology to create a master-slave configuration. Because each of the slaves are connected directly to the master, nodes may be added to the network without requiring hardware or software changes.In the master-slave configuration, slaves can only communicate with the master, and can send data only after receiving a data request from the master. Because each slave is separately connected to the master, a failure in any part of the network does not affect the rest of the network.

BEAN was developed by Toyota as a proprietary network before industry-wide automotive networks were available. Because LIN has now appeared as an industry standard and is also a low-speed, low cost network similar to BEAN, it is replacing BEAN in most newer Toyota vehicles.

LIN Characteristics

Local Interconnect

Network

LIN Replacing BEAN


LIN has a multiple slave network architecture with a message identification for multi-cast transmission between any network node. It shares some of the features of an AVC-LAN network except that a LIN master ECU contains a gateway function which has the capability to interface with higher-level networks such as CAN. This feature extends the benefits of networking all the way down to the individual sensors and actuators.

Local Interconnect Network (LIN)

Topology:• Master ECU is connected to the CAN network • Master serves as a gateway for up to 64 slaves• Single-wire voltage drive

ECUCAN

(e.g. Main Body ECU)

LIN

Master ECU

ECU

ECU ECU

SlaveECU

SlaveECU

SlaveECU

SlaveECU

LIN Gateway Function




Controller Area Network (CAN)

EPS ECUEngine ECU (ECM)

Air Conditioner Amplifier

SIL

DLC3

CAN-HCAN-L

J/C No. 1 J/C No. 2

: CAN Main Bus Line (High): CAN Sub-Bus Line (High): CAN Main Bus Line (Low): CAN Sub-Bus Line (Low): Serial Communication Line

Topology• Bus style with terminating resistors at each end• Sub-bus lines connect ECUs and sensors to the main bus line• Twisted-pair differential voltage drive

Terminating Resistors (120 ohm)

CAN HS = 500 kbps (max 1 Mbps)CAN MS = 250 kbps

Certification ECU

Meter ECU

Skid Control ECU

Main Body ECU

Airbag Sensor Airbag Sensor AssemblyAssembly

Steering Angle Steering Angle SensorSensor

Yaw Rate SensorYaw Rate SensorDeceleration Sensor

The Controller Area Network (CAN) was originally developed specifically for automotive applications by Bosch and later adopted as a standard by the International Standards Organization (ISO). It has since been adapted for use in elevators and medical device applications.Similar to BEAN, multiple ECUs are connected to a common CAN bus. However, CAN is not designed for use in a ring topology, and is limited to a maximum of 13 ECUs on a single network. To accommodate more ECUs, multiple CAN networks can be linked by Gateway ECUs.CAN uses twisted-pair wiring to carry matching high and low voltage signals for reliability and speed. It comes in two varieties– HS (high-speed, 500 kbps) and MS (medium-speed, 250 kbps).

The CAN bus uses 120 ohm resistors at each end of the bus to prevent signals from bouncing back and corrupting communications. Since each bus has two resistors between CAN high and CAN low, the resistance between the two CAN bus lines is approximately 60 ohms.

Controller Area Network

Terminating Resistors


AVC-LAN is a unified standard developed by six companies including Toyota Motor Corporation. The intention was to standardize signals such as audio signals, visual signals, switch indication signals and communication signals. The purpose for the standardization was to avoid the incompatibility that resulted when products from more than one manufacturer were combined in a single multimedia system.When the AVC-LAN is linked to other networks, a Gateway ECU (or a gateway function integrated in another ECU) is needed.

Audio Visual Communication -

Local Area Network

Audio Visual Communication –Local Area Network (AVC-LAN)

Topology:• Master-slave configuration using differential voltage drive• Broadcast, unicast, and multicast communication

Speed = 17.8 kbps

Audio Head Unit

Stereo Component Amp.

Stereo Component Tuner

Television Camera ECU

Navigation ECU

Audio and Rear A/C Panel Switch

Gateway ECU

Steering Pad Switch

Driver Side J/B ECU

BEAN AVC-LAN

Multi Display (Master)




Audio Head Unit

Stereo Component Amp.

Stereo Component Tuner

Television Camera ECU

Navigation ECU

Audio and Rear A/C Panel Switch

Gateway ECU

Steering Pad Switch

Driver Side J/B ECU

BEAN AVC-LAN

Multi Display (Master)

Audio Visual Communication –Local Area Network (AVC-LAN)

Control: • Each component has an ID. The one with the lowest ID is the master.

ID: 110

ID: 190

ID: 1F0

ID: 440

ID: 178

ID: 280

ID: 1F4 Note: IDs are hexadecimal numbers

An AVC-LAN system consists of audio units and ECUs that are connected in parallel. Each of these units has a switch to connect the unit to the communication bus. When the ignition switch is turned to the ACC position, the vehicle’ s AVC-LAN System Master Unit sends a registration request on the system’s LAN circuit. At that time, the mode control portion of the system transmits a physical address back to the Master Unit. The physical address is a three-digit code designation for each of the components of the system (such as the Navigation ECU, Television Camera ECU, Stereo Component Amplifier, etc.)The mode control portion of the system provides communication traffic control and transmits output ON, and output OFF instructions to each of these units when switching from one operation unit within the system to another. All of the components in the system transmit a logical address from each unit. The logical address is a two-digit code (in hexadecimal) that is assigned to each function for that unit (such as command switch, speaker beep, etc).The mode control portion of the system then verifies the connection and operation of each of the components.

The numeric IDs are given in hexadecimal numbers. Hexadecimal is the base-16 number system used by computers where A = 10, B=11, C=12, D=13, E=14, and F=15In vehicles with a multi display (ID = 110 or 118) , the multi display is the master. In vehicles without a multi display, the radio receiver (ID = 190) is the master.

AVC-LAN Protocol

NOTE


Certification ECU Driver Seat ECU Multiplex Tilt and Telescopic ECU

Outer Mirror Control

Tire Pressure Warning ECU Bus Buffer ECU

Gateway ECUs

Some ECUs have an integrated gateway function. If different types of networks connect to one ECU, you can assume it has a gateway function.

2009 Land Cruiser

Rear Heater Control Panel

Immobilizer Code ECU

Steering Lock ECU

CANV Bus (HS)

LIN

LIN

Main Body ECU (with

gateway function)

Main Body ECU (with

gateway function)

Navigation ECU*

Television Display*

Radio Receiver Assembly

Stereo Component Amplifier Assembly

Skid Control ECU Yaw Rate Sensor Assembly

Seat Belt Control ECU Steering Sensor

Skid Control ECU*

Clearance Warning ECU

ECM A/C Amplifier Assembly

Center Airbag Sensor Assembly

Combination Meter Assembly

Multi-Display*

Front Heater Control Panel

Sliding Roof ECUPower Window

ECU

CANMovement Control Bus (HS)

*: Option

DLC3

Network Gateway

ECU

Network Gateway

ECULIN AVC-LAN

CANMS Bus

LINCAN

AVC-LAN

Components on networks using different protocols can’t communicate directly with one another because they don’t “speak the same language.” To translate and relay messages between networks, Gateway ECUs were developed. A Gateway ECU also serves as the interface between vehicle networks and the diagnostic tester (via the DLC3 connector).In many systems, a major ECU (such as the Main Body ECU) may include a gateway function within it. If different types of networks connect to one ECU, you can assume it also serves as a Gateway ECU.

A vehicle may have multiple Controller Area Networks for a variety of reasons. • A CAN bus can have no more than 13 nodes. To link more than 13 components using CAN requires two or more networks. • CAN buses may be different speeds (HS or MS).• Multiple buses are often intentionally used so that a failure in one bus doesn’t disable components on other CAN buses.To link multiple CAN buses together, a CAN Gateway ECU can be used.

Gateway ECU

CAN Gateway ECU




Gateway ECU Functions

Communication: Provides communication link between multiple buses of the same protocol.

BEAN

CAN AVC-LAN

BEAN

BEAN

ECU

DLC3

Gateway ECU

Diagnosis: Stores DTCs for BEAN networks.

Interface: Translates messages from one protocol to another.

Customize: Enables the customize feature of BEAN networks.

DLC3

BEAN BEANBEANECUECU Gateway

ECU ECU

Gateway ECU

Gateway ECU

BEANECU ECU

ECU ECUAudio

The Gateway ECU connects buses of different protocols and DLC3, and manages communications between them. It also provides signal conversionbetween the BEAN, CAN, and AVC-LAN networks.Gateways also regulate the exchange of data between networks of the same protocol, such as two BEAN networks. Separate BEAN networks ensure that a failure in one network won’t disable all BEAN components.BEAN networks are connected to the DLC3 via the gateway and the gateway communicates with the diagnostic tester. The gateway does not interpret the messages; it simply transfers the Diagnostic Requests onto the BEAN and then transfers Diagnostic Responses from the BEAN onto ISO 9141 (the diagnostic protocol). If a malfunction occurs in the BEAN communication, DTCs are stored in the gateway memory. The gateway acts as a kind of firewall to prevent the entire system from being affected if one bus fails.The gateway enables the customize feature of BEAN networks.

Summary of Gateway ECU

Functions


CAN Gateway ECU Functions

Data destined for components on the other bus is relayed.

Data not intended for components on the other bus is not forwarded.

DTCs are stored in the CAN Gateway ECU.

ECU

CAN Gateway ECU

ECU

ECU

ECU

ECU

ECU

ECU

A CAN Gateway ECU has fewer but more specialized functions.

Compared to other Gateway ECUs, the CAN Gateway ECU’s functions are simplified:•Forward data from one bus to the other when the data is addressed to components on the other bus.•Restrict transmission of data to the other bus when the data is not addressed to any components on that bus.•Store DTCs for failure in components or communication lines.

CAN Gateway ECU Functions



Transmit/Receive Charts

Air Conditioning System Diagram

Transmitter Receiver Line Signal

A/C Amplifier

ECM BEAN/CAN

Heater Relay Control Signal

Magnetic Clutch Control Signal

Rear DEF Relay Control Signal

Idle Up Signal

Pressure Sensor Signal

External Variable Control Solenoid Current Signal

Multiplex Network Body ECU

BEAN Diagnostic Tool Response

Diagnostic Data

Accessory Meter Assy

BEAN / AVC-LAN

Indicator ON demand signal

DLC3

ECM

BEANAVC-LAN

CANECM

Gateway ECU

Accessory Meter Assy

Combination Meter Assy

Multiplex Network Body

ECU

Front Controller

A/C Amplifier

The transmit/receive charts in the Repair Manual can be very helpful in understanding the operation of a multiplex circuit. The example above is just a portion of the chart for the air conditioning system of a 2005 Avalon.These charts can be found in the System Diagram section of the Repair Manual for each system using multiplex communication.

Transmit/Receive Charts



BEAN Communication Signal

BEAN uses a single wire voltage drive protocol. The BEAN communication signal varies from zero to a nominal 10 volts. The circuit is at rest when at zero volts

BEAN Signal



BEAN Diagnosis

Communication line disconnection or open at 2 points

DTC No. Detection Item Detecting ConditionB1200 MPX Body ECU communication stop Communication with Gateway ECU

stopped 10 sec. or moreB1271 Combination meter ECU communication stop

Communication line short

B1214 Short to B+ in door system communication bus malfunction

When a +B short circuit is detected in the door system communication bus

B1215 Short to GND in door system communication bus malfunction

When a body ground short circuit is detected in the door system communication bus

Check DTC information

2008 Avalon

Examples

The Gateway ECU monitors communication on the BEAN and stores a DTC when it detects a network communication error (DTC B12XX). The Gateway ECU outputs only B12XX DTCs.Note that DTCs indicating “communication stop” typically mean there is a disconnection or open circuit that is isolating one more ECUs from the network. You can determine the possible locations of the open circuit by examining the wiring diagram and analyzing which ECUs are offline. Because short circuits disable the entire network, those DTCs do not identify a particular ECU. The diagnostic procedure for shorts involves disconnecting portions of the circuit until communication resumes. You then know the short is in the disconnected portion of the circuit.

BEAN Diagnosis



Defective combination meter ECU power supply or ground

BEAN Diagnosis – Open Circuit

DTC No. Detection Item Detecting Condition

B1271 Combination meter ECU communication stop Communication with Gateway ECU stopped 10 sec. or more

: Communication Circuit

Communication line disconnection or open at 2 points

Connector disconnected

Failure in Combination Meter ECU

Possible Causes

Body ECUBody ECU

A/C ECUA/C ECU Gateway ECUGateway ECU

Meter ECUWire harness open circuit

Defective inner communication

line in each ECU

Components connected to the BEAN in a ring style (daisy chain) have two paths for data flow around the ring, so a single open in the network does not stop communication. Two opens in the communication line, however, will isolate one or more ECUs.In the example above, the Combination Meter ECU has become isolated. The potential problem areas are:• A loss of power or ground to the Meter ECU• Failure inside the Meter ECU• Meter ECU connector disconnected• Two opens in the wire harness leading to the Meter ECU• Failures in the internal communication lines of the two ECUs connected to the Meter ECU

Open Circuit




BEAN Diagnosis – Short Circuit

DTC No. Detection Item Detecting Condition

B1215 Short to GND in door system communication bus malfunction

When a body ground short circuit is detected in the door system communication bus

Communication line short


Body ECUBody ECU


Meter ECUMeter ECU

The entire network is down due to the short.

When a communication line is short-circuited to B+, the entire line is 12V, and if short-circuited to ground, it’s 0V. Being unable to vary the voltage on the line, the Gateway ECU cannot communicate with any ECUs so it is impossible for it to determine the location of the short.To locate the short, disconnect each ECU one by one and check what DTC is output.

Short Circuit


BEAN Diagnosis – Short Circuit (Step 1)

“A”

“B”

“C”

“D”

Begin by disconnecting the first ECU, then checking if network communication resumes.

If network communication resumes after removing the Meter ECU, the short is in this ECU.

If communication does not resume, the short is still in some other part of the network.


Body ECUBody ECU


Meter ECU

Working around the ring starting with the first ECU past the Gateway, begin disconnecting ECUs one by one. When the ECU with the short is disconnected, network communication will resume.To determine when the network is communicating again, you can connect a DVOM or oscilloscope to the BEAN circuit at the Gateway ECU. When voltage or a signal reappears on the circuit, the most recent component disconnected is the one with the short..Another way to check for communication is to examine DTCs after an ECU is disconnected. In this example, the Meter ECU is disconnected first.If DTC 1215 (communication line short) is still present, then the Meter ECU is not the problem; the short is still in the part of the circuit connected to the Gateway ECU. Continue to the next step.• If DTC 1271 (Meter ECU stop) occurs, then the short circuit is no longer present in the network and it is working again. This means the short must be in the disconnected Meter ECU. Replace it.

Don’t disconnect the Gateway ECU because that’s where the DTCs are stored. When DLC3 is connected to the Gateway ECU, disconnecting the Gateway from the rest of the network sets DTCs for all the other ECUs because the Gateway can no longer communicate with any of them.

Short Circuit Step 1

NOTE





If the fault is not found, disconnect the next ECU and recheck for communication.

If communication resumes after the Body ECU is disconnected, the short is in harness B” or in the Body ECU. Reconnecting the Meter ECU will tell you where the short is (Step 3).

“A”

“B”

“C”

“D”

If communication does not resume, the short is still in some other part of the network. Reconnect the Meter ECU, then disconnect the A/C ECU (Step 4).



Body ECU Meter ECU

Continuing trouble shooting this example, disconnect the next ECU after the Meter ECU and check if the communication signal reappears.If checking DTCs:• If DTC 1215 (communication line short) is still present, then the harness “B”and the Body ECU are not the problem. The short is in the part of the network still connected to the Gateway ECU. Continue to step 4.• If DTC 1271 (Meter ECU stop) and DTC 1200 (Body ECU stop) occur, then the short circuit is no longer present in the network. Since you already ruled out a problem with the Meter ECU, this means the fault must be in the disconnected harness “B” or in the Body ECU. To diagnose which, continue to step 3.




If fault is found, isolate the location by reconnecting the first ECU and rechecking for communication.

If communication continues, the short is in the Body ECU that is disconnected from the network.

If communication stops when the Meter ECU is reconnected, that means the short is in the harness that was just reconnected to the network.

“A”

“B”

“C”

“D”



Meter ECUMeter ECUBody ECU

To determine if the problem is in harness “B” or the Body ECU, reconnect the Meter ECU.If communication stops, the short is in harness “B”. If communication continues, the short is in the Body ECU.If checking DTCs:• If DTC 1215 (communication line short) occurs again instead of DTC 1200 (Body ECU stop), then the short has been reconnected to the part of the circuit connected to the Gateway ECU. It has to be in harness “B”. Replace it..• If DTC 1200 (Body ECU stop) remains, the short circuit has been isolated from the network. The only part not connected to the network is the Body ECU. Replace it.






If the fault wasn’t found, continue isolating the problem by disconnecting the next ECU and rechecking for communication.

If communication resumes, the short is in harness “C” or the A/C ECU. Reconnect the Body ECU and recheck for communication (Step 5)

If communication does not resume, the short is still in part of the network connected to the Gateway ECU

“A”

“B”

“C”

“D”


Gateway ECUGateway ECU

Meter ECUMeter ECUBody ECU

A/C ECU

Not having found the fault yet, disconnect the next ECU after the Body ECU and recheck for network communication.If communication resumes, the fault is in either harness “C” or the A/C ECU because these two components have been removed from the network. Go to step 5 to determine which component is at fault.If communication does not resume, reconnect the Body ECU, and go to step 6.If checking DTCs:• If DTC 1215 (communication line short) is still present, then the harness “C”and the A/C ECU are not the problem because they are no longer connected to the Gateway ECU. Continue to step 6.• If DTC 1200 (Body ECU stop) and B1262 (A/C ECU stop) occur, then the short circuit is no longer present in the network. This means it must be in the disconnected harness “C” or in the A/C ECU. To diagnose which, continue to step 5.




If fault is found, isolate the location by reconnecting the previous ECU & rechecking DTCs.

If DTC 1262 (A/C ECU stop), then the short is in A/C ECU.

If DTC 1215, then the short is in the part of the network that was just reconnected to the Gateway ECU.

“A”

“B”

“C”

“D”


Body ECUBody ECU

Gateway ECUGateway ECU

Meter ECUMeter ECU

A/C ECU

To determine if the problem is in harness “C” or the A/C ECU, reconnect the Body ECU and check for communication.If communication does not resume, the short is in harness “C” that was just reconnected to the network.If communication does resume, the short is in the S/C ECU that is still disconnected from the network.If checking DTCs:• If DTC 1215 (communication line short) occurs again, then you’ve reconnected the short to the communication circuit. Since you already ruled out the Body ECU as the problem, it must be in harness “C”. Replace it.• If only DTC 1262 (A/C ECU stop) is present, then the short circuit is no longer present in the network. This means it must be in the disconnected A/C ECU. Replace it.






If the fault wasn’t found, it is in harness “A” or “D,” or in the Gateway ECU.

All other parts of the circuit have been eliminated except “A”, “D” and the Gateway ECU.

Test the two harnesses for a short. If no short is found, replace the Gateway ECU.

“A”

“B”

“C”

“D”


Body ECUBody ECU


Meter ECUMeter ECU

The only remaining locations for the short are in harness “A” or “D,” or in the Gateway ECU.• Test wire harnesses “A” and “D” for a short, and replace if needed.• If the short is not in either wire harness, replace the Gateway ECU.



BEAN Diagnosis by Split-Half Method

When many ECUs are connected to the bus, disconnect half the bus to save time.

Disconnect Disconnect

ECU “A”ECU “A” ECU “B”ECU “B” ECU “C”ECU “C” ECU “D”ECU “D” ECU “E”ECU “E”

Gateway ECUGateway ECU ECU “I”ECU “I” ECU “H”ECU “H” ECU “G”ECU “G” ECU “F”ECU “F”

Disconnecting ECUs one at a time can be time consuming if the network has a large number of ECUs. To save time, isolate half the network by disconnecting an ECU nearest the Gateway, and another farthest away.• If communication resumes, the short is in the disconnected part of the network.• If communication does not resume, the disconnected ECUs are normal and the short is in the other half. Knowing which half of the network to diagnose, proceed by disconnecting and connecting ECUs one at a time until you find the trouble location.

Diagnosing a Large Network




BEAN Diagnosis

If there is no multiplex communication system DTC, check the relevant ECUs using Techstream.

Data List – Check switch or sensor to find:• Switch or sensor malfunction• Malfunction in an ECU input circuit

Active Test – Check actuator to find:• Actuator malfunction• Malfunction in an ECU output circuit

When diagnosing a problem for which there are no BEAN communication DTCs (B12xx), use Techstream to test the ECUs related to the problem for proper function.• Data List enables you to test the inputs to the ECU. If the ECU is not seeing the correct switch or sensor values, you can isolate the problem to the switch/sensor, switch/sensor circuit or the ECU itself.• Similarly, Active Test enables you to test the ECU outputs. This can narrow a problem down to an actuator circuit, an actuator or the ECU.

Because BEAN is a slow-speed network, the Data List may update very slowly. To speed results, make a custom list of just those data items being monitored.

Diagnosis with Techstream

NOTE


Diagnosing a BEAN Open Circuit

When the signals at two points in the same BEAN circuit are not identical, there is an open between those two points.

When a BEAN network is operating normally, oscilloscope probes can be placed at any point on the network and the signal patterns will be perfectly identical. That’s because the network is continuous and the signal at any point is the same. However, an open circuit in a bus segment of a BEAN network separates the network into two parts. Similarly, two opens in the ring portion of the network also separate the network into two parts. Now the network is no longer continuous.Though separated into two different networks, the ECUs on each half continue to communicate with each other. Being separate networks, however, the communication on each half is now unique. The oscilloscope trace on one half is different from the trace on the other half.Knowing this can help you two ways in diagnosis.

• If you find the signals on two points of a BEAN network are different, you know those points are divided by an open circuit (or two).

• As you move one of the probes closer to the other, when the signals become identical, you have just passed over the location of the open circuit.

Diagnosing a BEAN Open Circuit with an

Oscilloscope



Worksheet

BEAN Network DiagnosisClassroom Worksheet:

This worksheet introduces you to BEAN network operation and fault diagnosis.

Instructor Demo

The instructor will demonstrate how to use the PicoScope for diagnosing a BEAN network.


NOTES:



LIN Communication Signal

Similar to BEAN, LIN also uses the single wire voltage drive protocol with a signal voltage range between zero and a nominal 12 volts. The circuit is at rest at the higher voltage.

LIN Signal



LIN Diagnosis

Diagnosis is similar to BEAN:• For shorts, disconnect connectors and recheck DTCs.• For opens, follow the DTCs.

2008 Highlander HV

Main Body ECU

(Instrument Panel

Junction Block)

Main Body ECU

(Instrument Panel

Junction Block)

Smart Key ECU Assembly

Smart Key ECU Assembly

Steering LockECU

Steering LockECU

Power Window ECU

Power Window ECU

Sliding Roof Control ECUSliding Roof Control ECU

Immobilizer CodeECU

Immobilizer CodeECU

LIN (Certification Bus)

LIN (Door Bus)

Diagnosing a LIN circuit is similar to diagnosing a BEAN circuit, except LIN does not use a ring or daisy chain configuration.When a communication line is shorted to ground, the network cannot communicate with any ECU. To isolate the location of the fault:• Disconnect connectors and recheck DTCs to isolate the part of the circuit with the short.With an open, DTCs guide you to the circuits to check. Possible causes are:• Connector disconnected• Defective ECU power supply or ground• Open in wire harness• ECU failure

LIN Diagnosis



Worksheet

A/C LIN Interface

In this worksheet you will monitor and diagnose the A/C Control Assembly operation, and LIN communication using the Techstream unit, TIS and a PicoScope.


NOTES:



CAN Communication Signal

CANH: 2.5v to 3.5v

CANL: 2.5v to 1.5v

CAN uses the two-wire differential drive protocol. The signal on the CAN High (CANH) wire ranges from 2.5v to 3.5V, while the signal on the CAN Low (CANL) wire ranges from 2.5v to 1.5V. Note that the two signals are mirror images with CANH going high (to 3.5V) at the same moment CANL goes low (to 1.5). When both signals are 2.5V, the circuit is at rest.

CAN Signal



ECU ECUECU

CAN Diagnosis – Shorts

Short between CAN-H and CAN-L:

No ECUs can communicate.

Short

Communication is not reliable.

Sub Bus

Main Bus

ECU ECUECU

ECU ECUECU

Short CANH to ground:

ECU ECUECU

No ECUs can communicate.

Short to B+ (CANH or CANL):

B+

Short CANL to ground:Communication is not reliable.

Note hyperlinks to circuit traces.

The CAN bus uses twisted-pair wiring for reliability. At each end of the CAN bus, the wires are connected together by a 120 ohm terminating resistor. The purpose of the resistors is to reduce noise in the circuit. The resistors may be located inside ECUs or junction connectors.

When the bus wires are shorted together at any point on the bus, it is impossible to generate a differential voltage on each wire for communication. Thus, the entire bus goes down.

Even when the network is down, each ECU continues to attempt communication. If you isolate an ECU from the short and the problem is not in the ECU, an oscilloscope will show it still generating CAN signals.

When a connection to B+ brings CANH high, or when a connection to ground brings CANL low, there is still the appearance of communication on the circuit. In the first case, CANL can still be brought low to create a voltage differential, and in the second case, CANH can still be brought high. Though communication on the circuit is compromised, ECUs may still appear in the CAN bus check in either case.On the other hand, bringing CANH low by grounding it, or bringing CANL high with a short to B+ renders the circuit incapable of generating a voltage differential. These are the cases when the ECUs do not show up in the CAN bus check.

Wave forms for various short circuit conditions appear in the appendix.

CAN Diagnosis

Short Between CANH and CANL

NOTE

Short to B+ or Ground



CAN Diagnosis – Opens

On Main Bus: Communication is not reliable on each half of the network.

Open

Open on both CAN-H and CAN-L:

ECU ECUECU

Open on just CAN-H or CAN-L:

ECUECUECU

Open in CANH or CANL

On Sub Bus: Affected ECU can’t communicate.

ECUECU

Open

Open in CANH or CANL

ECU ECU ECUECU

On Main Bus: Communication is not reliable.

On Sub Bus: Communication with the affected ECU is not reliable.

Note hyperlinks to circuit traces.

When an open occurs on the CAN bus, the effect depends on whether the open is on the main bus line or a sub bus line. An open on the main bus affects the entire bus, but an open on a sub bus line only isolates the ECU(s) on that sub bus.

Despite an open, the ECUs connected together are still trying tocommunicate, but the break in the network introduces considerable noise into the signal. Therefore, communication becomes unreliable.

Wave forms for various open circuit conditions appear in the appendix.

Opens

NOTE



CAN BUS Check

Using Techstream to perform a CAN bus check quickly identifies any ECUs that are not communicating. Comparing these ECUs to the multiplex circuit diagram from the EWD can potentially help identify possible problem locations before performing vehicle diagnostics.

When analyzing the multiplex circuit diagram to locate the ECUs that are not communicating, also note the location of DLC3. A problem between the network and DLC3 can make it appear the entire network is down.Also, when the vehicle has more than one CAN network, DLC3 is directly connected to only one of them. By analyzing the ECUs that are communicating, you can determine which CAN network is experiencing trouble.

CAN Bus Check

Location of DLC3



CAN Terminating Resistors

Know where the terminating resistors are located.

Disconnecting them will cause network communication to become unreliable.

HS Bus MS Bus

The CAN high and CAN low communication lines are connected at each end by a terminating resistor. This resistor helps to stabilize voltages on the lines and prevent “echoes.”The terminating resistors are almost always inside two of the ECUs on the network. (In some vehicle models, a terminating resistor may be located inside a junction connector.)As the illustration above shows, disconnecting either of the ECUs containing an HS bus terminating resistor would create an open in the CAN bus and take the bus down.All of the other components on the CAN HS bus are connected by sub bus lines. Therefore these ECUs can be disconnected from CAN without creating an open in the main bus line.

Terminating Resistors



CAN diagnostic procedures in the Repair Manual call for various resistance tests that can be useful in identifying shorts and opens in the bus line. To perform resistance testing on the CAN bus, the ignition must first be cycled OFF.

After turning the ignition off, it may take up to several minutes for capacitors to fully discharge and the resistance reading to stabilize. Any readings obtained before the circuit has stabilized will not be accurate.Resistance measurements will change slightly when Techstream is connected to the network via DLC3.

Resistance Tests on CAN Circuits

NOTE

CAN Resistance Tests

Check Bus Line (CANH – CANL)

A

Check Bus Line (CANH/L - BAT)

Open in CAN Bus LineB

Short in CAN Branch LineC

Short of CAN Bus line to BATNG

OK!

A OK! (54 to 69 Ohm)B NG (70 Ohm or more)C NG (Less than 54 Ohm)

CANH – BAT OK!CANL – BAT (6k Ohm or more)

Check Bus Line (CG – CANH/L)

CG – CANH OK!CG – CANL (200 Ohm or more)

NG Short of CAN Bus line to CG

OK!

Check Communication Malfunction DTC (Past DTC)

Does 60 ohms between CANH and CANL mean the network is OK?



CAN Resistance Tests

9 10 11 12 13 14 15 16

1 2 3 4 5 6 7 8

BAT

CANHCG

CANL

Hi LODLC 3

ECU ECU ECU

• CANH to CANL

• CANH to BAT

• CANL to BAT

• CG to CANH

• CG to CANL

When it comes time in the diagnostic process to measure the resistance between CANH and CANL, it doesn't take but a few extra moments to obtain all the other resistance measurements, too. Doing so can provide a more complete picture of the bus status before arriving at a conclusion regarding the source of a problem.

Before making resistance measurements between the CAN bus and B+ or ground, disconnect the negative battery cable. This prevents obtaining resistance readings through alternate paths.

When analyzing resistance measurements, more than one reading may be out of spec. For example, there may be a 73 ohm reading between CANH and CANL and a 0.3 ohm measurement between CANL and CG. If the only measurement taken was the out-of-spec resistance of CANH to CANL, the diagnostic flow chart on the previous page would indicate an open circuit. In reality, an open circuit would create a very high ohm reading. By making the other measurements, the 0.3 ohm reading between CANL and CG suggests a short to ground. This would most likely be the problem rather than the slightly out-of-spec 73 ohm reading between the bus lines.

When testing resistance at the DLC3 connector, keep in mind that in models with a more than one CAN bus, the DLC3 terminals may be testing only one of the buses. To test other CAN buses, it may be necessary to use a different connector.

Resistance Tests on CAN Circuits

NOTE

NOTE



Worksheets (1 of 3)

CAN DiagnosisClassroom Worksheet:In this worksheet you will build a strategy to diagnose a CAN network fault using the EWD, a Techstream CAN bus check, and the information provided.

2006 RAV4 Multiplex Circuit Diagram (PDF)>>>>

Instructor DemoCAN Resistance Test PrecautionsIn the shop, the instructor will demonstrate how improper methods can result in incorrect CAN resistance measurements.


NOTES:



Worksheet (2 & 3 of 3)

CAN Sub Bus DiagnosisShop Worksheet:In this worksheet you will use the EWD and Techstream’s CAN Communication Bus Check to develop a strategy to diagnose CAN sub bus faults.

CAN Main Bus FaultsShop Worksheet:In this worksheet you will:• Use an ohmmeter and a PicoScope to

observe CAN High and CAN Low• Diagnose a short to ground and an open

circuit on CAN High and CAN Low• Short CAN High to CAN Low to observe

the results.


NOTES:



AVC-LAN Communication Signal

Differential Voltage Drive• TX+ (similar to CANH)

• TX- (similar to CANL)

TX+ and TX- are both pulled high. The rulers show the differential voltage is greater than 120mV.

(+5V Scale, 5ms per division, x4 zoom)

2v to 3v

AVC-LAN uses differential voltage drive similar to CAN. However, the high and low voltage signaling circuits – similar to CANH and CANL - are referred to as TX+ and TX- in AVC-LAN devices.Also similar to CAN, the ends of the TX+ and TX- lines are joined by 120 ohm resistors.Whereas the CAN bus line idles at 2.5V, the AVC-LAN idles at around 2V. When communicating, AVC-LAN pulls the voltage high on both TX+ and TX-. The line voltages have to differ by more than 120mV for the AVC-LAN system to recognize communication.

AVC-LAN Signal



Vehicle Condition Procedure

• SPD 0 km/h

• ACC or IG ON*

Method 1While pressing the “INFO”button, alternately turn the light control switch from OFF to TAIL 3 times

Method 2While in the display adjustment screen, alternately touch the upper and lower parts of the left side of the screen 3 times

AVC-LAN Diagnosis

*To quit the diagnostic mode, turn to IG OFF.

Starting Diagnostic Mode (with Multi Display)

TAIL

OFF

+

Note: On some vehicles 2010 and beyond, AVC-LAN DTCs can be retrieved using Techstream.

Some vehicle models have AVC-LAN that functions independently of any of the other vehicle networks. The AVC-LAN in other models, however, may communicate with other vehicle networks through a Gateway ECU or other ECU with a gateway function. Before diagnosing the AVC-LAN, first be sure any other networks the AVC-LAN connects to are functioning properly.

AVC-LAN Diagnosis



AVC-LAN DTCs

Code: 01-E0Logical Address DTC

Physical Address Connection

Confirmation #

Occurrence Count

Sub-Code: 110-00- 4

Physical Address

178Navigation ECU

110Multi Display

190Radio and Player

440Stereo Component

Amplifier

Logical Address

Navigation ECU01 = Communication control58 = Navigation ECU80 = GPS Receiver

Multi Display01 = Communication control34 = Front passenger monitor

Stereo Component Amplifier01 = Communication control61 = Cassette tape player sw.63 = On-dash CD changer

DTC

E0 = “Registration complete” signal from master device cannot be received

Connection Confirmation #• The number of minutes after

power-up when the DTC occurred

Occurrence Count• The number of times the

DTC has been detected

Note: AVC-LAN codes are vehicle specific. Always check the Repair Manual for the vehicle being serviced.

AVC-LAN has a fairly robust self-diagnostic capability with diagnostic trouble codes consisting of five parts:Logical Address. The logical address code ( a hexadecimal number) does not refer to a component; it refers to a function within a component. The Navigation ECU, for example, has a Navigation ECU function (logical address = 58) and a GPS Receiver function (logical address = 80). Other components have their own unique functions with their own unique logical addresses. An exception is the Communication Control function which every AVC-LAN component has. This function’s logical address is 01. DTC. The DTC is a hexadecimal number that defines the specific problem. For each DTC, the Repair Manual has an explanation of the meaning and the corrective action or additional diagnostic steps.Physical Address. This hexadecimal number corresponds to specific AVC-LAN components such as the Navigation ECU, audio head unit, stereo amplifier, multi-display, etc. Connection Confirmation Number. Upon power-up, the AVC-LAN master ECU checks all the slaves once per minute. The connection confirmation number increases by one after every check. When a DTC is detected, the connection confirmation number is included with the DTC information to indicate when the fault occurred in relation to power-up. This can be useful in determining the sequence in which DTCs occurred.Occurrence Count. Provides a count of the number of times a DTC has been detected.

AVC-LAN DTCs



Worksheet

AVC-LAN Inspection Shop Worksheet:In this worksheet you will create, monitor and diagnose a Stereo Component Amplifier malfunction involving an AVC-LAN circuit.


NOTES:



Other Multiplex CircuitsBUS connectors in air conditioning servo motor circuits illustrate the advantages of a simple multiplex circuit.

With Bus Connectors

Pulse-type Servo motors

BUS ConnectorCommunication/Driver IC

A/C Amplifier

Communication IC

CPU

One 3-wire harness

Without Bus Connectors

Servo motors

Four 5-wire harnesses

A/C AmplifierDrive IC

CPU

Drive IC

A/CM M MM

A/CM M MM

Although BEAN, LIN, CAN, and AVC-LAN are the most frequently used multiplex protocols in automobiles, other automotive systems may gain the advantages of multiplex communication by implementing their own special purpose protocols.Dynamic laser cruise control is one example of a circuit that uses serial communication that is not BEAN, LIN, CAN or AVC-LAN. The laser sensor and Distance Control ECU use their own special purpose multiplex protocol because of the complex communication required between them.The significance of knowing this is that when you encounter a circuit described as “serial”, you’ll know to expect a fluctuating communication signal on that line instead of a fixed voltage.

An air conditioning servo motor circuit is another good example of using multiplex circuits to reduce wiring. The typical connection between the A/C amplifier and an ordinary servo motor requires five wires:• Two wires to the motor – necessary so forward or reverse current can be supplied to control motor direction.• Three wires to the sensor circuit to determine motor position and direction.To reduce the wiring between the servo motors and the A/C amplifier, pulse-type servo motors use a communications chip built into the servo motor connector. This chip, called a BUS connector, communicates with the A/C amplifier using serial data (multiplex) communications. In this configuration, only three wires are needed:• Power• Ground• Communication signal

Other Multiplex Circuits

A/C Servo Motor Circuits



BUS ConnectorsBUS Connectors with built-in communication/driver ICs allow the use of pulse-type servo motors and require less harness wiring.

Bus Connector

With Bus Connectors

Pulse-type Servo motors

BUS ConnectorCommunication/Driver IC

A/C Amplifier

Communication IC

CPU

One 3-wire harness A/C

M M MM

Note: If the color-coded connectors are not matched to the correct servo motors, the wrong motors will operate.

IC

The BUS connectors are sequentially arranged on a single harness to yield a bus network topology. Each BUS connector controls its motor’s operation by translating serial data from the A/C amplifier on the communication signal line. It then interprets pulses from the A, B, and GND contacts on the servo motor, converts them into serial data and transmits position information back to the A/C amplifier.All the BUS connectors share the same communication line, so the serial data flowing to and from the connectors must include a connector ID. This ID enables the connector to ignore A/C amplifier signals meant for another servo motor, and enables the A/C amplifier to determine which connector is transmitting its motor position information. Because of this, if the connectors are not matched to the correct servo motors, the wrong motors will operate.

Some newer vehicles have as many as 12 AC servo motors operating on three unique BUS connector networks. In these vehicles, this special purpose multiplex protocol saves a considerable amount of wiring, contributing greatly to lighter weight, less expense, and greater reliability.

BUS Connectors

NOTE



Pulse-Type Servo Motors

Pulse-type servo motors transmit two ON/OFF signals to communicate damper position and movement direction.

Servo MotorABGND

A

B

A

B

High

Low

High

Low

Contact Points Printed Circuit Board

Conduction

GND

Also called pulse pattern type servo motors, these motors use a printed circuit board that rotates with the motor shaft to signal motor direction and position. As the motor turns, the contact points at A and B open and close a circuit to create a coded pulse pattern that indicates the position of the damper doors.Because the output signals from the motor are digital (ON/OFF), the communication chip that relays these signals does not need to perform analog-to-digital conversion. This makes the communication chip much simpler, smaller, and less expensive.

Pulse-Type Servo Motors



Worksheet

A/C Bus Servo Motor Operation & Diagnosis

Shop Worksheet:In this worksheet you will monitor Bus Connector and Servo Motor operation using Techstream DATA LIST and a PicoScope to deduce communication problems with the A/C System.


NOTES:






• Engine Immobilizer• WORKSHEET: Immobilizer System• Power Distributor• Smart Junction Box (MICON)• HID Headlights• Dynamic Laser Cruise Control

Section 8 Topics

Electronic Systems



Key Cylinder

Transponder Key Coil Transponder Key

Amplifier

SecurityIndicator

Light

DLC3

TransponderKey ECU

ECM

Communication

Immobilizer Function

Prohibits the engine from starting unless an authorized ignition key is used.

ID code stored in key must match code stored in ECU.

Disabled until ECM receives “OK” from Transponder Key ECUBlinks until authorized

key is in key cylinder.

Transponder Chip

Ignition Key

Ignition

Fuel

The engine immobilizer system is designed to prevent the vehicle from being stolen. When the immobilizer system is set, the ECM disables the fuel delivery and ignition systems. Only an authorized key can unset the immobilizer.The Transponder Key ECU assembly stores the codes of authorized ignition keys. When an authorized key is used to start the engine, the ECU sends a signal to the ECM to unset the immobilizer and permit fuel delivery and ignition.

Engine Immobilizer Function



Immobilizer System Operation

1. Detects unlock warning switch is on when key is in ignition

2. Activates antenna coil

3. Faint electric wave sent

4. Key ID code returned

5. ID code signal amplified and sent to ECU

6. ECU compares key ID code to registered codes.

If codes match:

7. Cancels immobilizer

8. Turns off indicator light

1234

5

6

7

8

ECU Logic

ECM

TransponderKey ECU

TransponderKey

Amplifier

Unlock Warning Switch (Key Cylinder)

Front Door Courtesy Light

Switch (LH)

Security Indicator Light

Antenna Coil

When a key is inserted in the key cylinder, the Transponder Key ECU detects the unlock warning switch is closed and sends a signal to activate the antenna coil in the transponder key amplifier. The antenna generates a faint electric wave activating the transponder chip in the key grip to transmit its ID code. The transponder key amplifier receives and amplifies the ID code signal, then transmits it to the Transponder Key ECU. The ECU compares the key’s ID code to the registered codes stored in its memory. If the codes match, the ECU sends a signal to the ECM to unset the immobilizer and switches off the security indicator light.

For the immobilizer system to operate, authorized keys must be registered with the Transponder Key ECU. The system provides three types of key code registration procedures.New Key Registration. This procedure is used if the registered master keys are lost, and when the Transponder Key ECU must be replaced for other reasons. An initial set of keys can be automatically registered immediately after the new ECU is installed. Additional Key Registration. New keys (up to a certain total number of keys based on vehicle model) can be added to those already registered in the Transponder Key ECU.Key Code Erasure. For lost keys, key codes can be erased. This procedure erases all codes except the master key. The remainingauthorized keys must be reregistered.

Engine Immobilizer Operation

Key Code Registration



Sub key indication (on for 2 sec.)

Immobilizer is set Immobilizer is unset

Key recognized

Immobilizer is set Immobilizer is unset

Security Indicator Light

Master key indication (light goes off)

…

…

…

…

…

…

No key or unregistered key (keeps blinking)

Immobilizer is set

The difference between a master key and a sub key is that a sub key cannot be duplicated. This is a security feature that helps customers feel safer about leaving a key with parking attendants.You can distinguish between a master key and sub key by observing the security indicator light when the key is inserted in the ignition switch.

• When a master key is placed in the ignition switch. The indicator light turns off.

• When a sub key is placed in the ignition switch, the indicator light remains illuminated for 2 seconds before turning off

Master Keys and Sub Keys



Automatic Key Code RegistrationIndicator codes during automatic key code registration:

Code 2-1: Registration failed (bad key)

Code 2-3: Maximum number of keys already registered

Code 2-2: Key has already been registered

Blinking: Everything is operating normally

When the Transponder Key ECU is replaced, the new unit is preset to automatically register keys. To take advantage of automatic key code registration:

• After replacing the transponder key ECU, insert the first key into the ignition key cylinder. It takes about one second for the transponder key ECU to register the key’s code.

• Remove the key and insert the next key.• Repeat until all keys have been registered.

If an error occurs during automatic key code registration, the security light blinks a two-digit code:Code 2-1: Key code registration failed, most likely because a code could not be read from the key’s transponder chip. The key should be discarded. Code 2-2: The key has already been registered.Code 2-3: The maximum number of keys have already been registered.

Automatic key code registration ends automatically after the maximum number of keys have been registered. If registering fewer than the maximum number of keys, the automatic registration process has to be terminated manually.

• Use Techstream to end automatic key code registration.• Turn the ignition switch ON and OFF five times within 10 seconds to

force automatic key code registration to end.

Failing to terminate key code registration can result in abnormal system operation.

Automatic Key Code Registration

Watch for Error Codes

Ending Automatic Registration

NOTE



Configuration in Earlier Models

In earlier models, the immobilizer functions are built into the ECM.

2001 Avalon

Engine immobilizer was introduced in the 1998 model year. The first vehicles with this feature have the immobilizer functions built into the Engine Control Module. This configuration exists in model years as late as 2004.

Configuration in Earlier Models



Configuration in Later Models

2007 Tundra

In later models, the immobilizer functions are controlled by a separate Transponder Key ECU.

In later models, a separate Transponder Key ECU was added to control the immobilizer functions in place of the ECM. The advantage of a separate, special ECU is that it is less expensive to replace than an ECM in the event of lost keys or an ECU malfunction.

Configuration in Later Models



TIS Immobilizer Reset

Immobilizer reset is not supported on all vehicles. Refer to the Support Chart for more information.

Because of the original system design for the immobilizer function, losing all the keys to the vehicle meant that the ECM or Transponder Key ECU had to be replaced. Later systems were modified so that the ECM or Transponder Key ECU could be reset to accept registration of new keys.Resetting the immobilizer to accept new keys requires obtaining a passcodethrough TIS. For security reasons, only Master Technicians and MDTs are authorized to request an immobilizer reset passcode. For theft prevention and security monitoring, each time a passcode is requested, it is logged into a national database.Once a passcode is obtained, it’s entered into the ECU through Techstream or a scan tool. When the ECU is successfully reset, the master key in the ignition becomes registered to the vehicle and all previous key codes are erased.

Immobilizer Reset



Immobilizer Reset Support Chart

From TIS Immobilizer Reset Page

The blue boxes on the support chart indicate which vehicle models have the immobilizer reset feature. The legend at the top of the chart describes applicable TSBs.Immobilizer systems that do not have immobilizer reset are indicated by the white boxes. In these vehicle models, either the Transponder Key ECU or ECM must be replaced if all the keys to the vehicle are lost. In these cases, whether the ECM or Transponder Key ECU must be replaced depends on the system configuration. If the vehicle has a separate Transponder Key ECU, then that is the component that must be replaced. If the immobilizer functions are controlled within the ECM, then the ECM must be replaced.PANT Bulletin GI03-09 (referenced next to the white square in the legend) describes conditions under which the ECU or ECM replacement cost can be subsidized.

Immobilizer Reset Support Chart



ECM Communication ID Registration

In vehicles with a separate Transponder Key ECU, the ECM Communication ID must be registered whenever the ECM or Transponder Key ECU is replaced.

1. Using SST, connect TC to CG.

2. Turn the ignition switch ON (do not start the engine) and leave it for 30 minutes.

3. Turn the ignition switch OFF and disconnect TC and CG.

4. Check that the engine starts.2005 Avalon

Example Procedure:

CG

TCDCL3

SST

For security reasons, immobilizer systems with a separate Transponder Key ECU are designed so that the vehicle will not start if either the ECM or ECU have been replaced. This security is provided by a unique ECU communication ID stored in both the ECM and Transponder Key ECU.Therefore, when either unit is replaced, the ECU communication ID has to be registered between them.

The code registration procedure described above is an example that may not apply to all vehicles. Be sure to refer to the Repair Manual for the correct procedure for the vehicle being serviced.

ECU Communication ID

Registration

NOTE



DTC Check/Clear

Immobilizer diagnostic methods and procedures may vary between vehicle models. Examples:

Vehicle Model To check DTCs w/check wire on DLC3

To clear DTCs w/o Techstream Techstreamsupported?

2005 Avalon • TC to CG • Remove the EFI No. 1 fuse Yes

2006 Sequoia • TC to CG for DTC 99• CG to OP3 for other DTCs

• Remove the ECU-B fuse and EFI No. 2 fuse from the engine room J/B for 1 minute or more.

No

2006 Tacoma • Not supported • Not supported Yes

2006 Tundra • CG to OP3 • Remove the ECU-B fuse from the driver side J/B for 1 minute or more.

Yes

CG

TC

OP3

DLC3

1

9 10 111213 1415 16

2 3 4 5 6 7 8

While the concepts of immobilizer components and operation are similar among all systems, the specifics of each system can vary significantly. The example above demonstrates how different the diagnostic methods and procedures can be between different models. The bottom line is that when diagnosing the immobilizer system, it’s especially risky to assume that one vehicle model is the same as another. Always refer to the repair manual for the specifics of the vehicle being serviced.

Be Wary of Differences between

Models



Transponder Key ECU

Input Signals:• KSW• CODE• EFII• CTY

Output Signals:• VC5• TXCT• IND• EFIO

2007 Tundra

In diagnosing an engine immobilizer malfunction, you may need to verify the Transponder Key ECU is receiving the correct input signals and is sending the correct output signals. Remember that in earlier model vehicles without a Transponder Key ECU, you’ll be verifying the immobilizer system signals flowing into and out of the ECM.You can identify the inputs and outputs using the system description and looking at the wiring diagram and TERMINALS OF ECU section of the Repair Manual. For our example, we’ll be using the 2007 Tundra to illustrate diagnostic concepts. Note that these may not translate exactly to other vehicle models.Inputs:KSW – ignition key cylinder unlock warning switchCODE – key ID code from transponder key amplifierEFII – ECM communication input signalCTY – front door courtesy switch LH (required for registration only)Outputs:VC5 – five-volt power supply to transponder key amplifierTXCT – communication signal to transponder key amplifierIND – security indicator light signalEFIO – ECM communication output signal

Analyzing ECU Input and Outputs



Transponder Signals

KSW

VC5

TXCT

CODE

2007 Tundra

KSW. When a key is inserted in the key cylinder, the key switch closes. The voltage on KSW drops to zero, alerting the Transponder Key ECU.VC5. The Transponder Key ECU immediately supplies power to the transponder key amplifier so it can operate. TXCT. The Transponder Key ECU commands the transponder key amplifier to begin pulsing for the key code. CODE. The amplifier sends the code to the Transponder Key ECU.After the transponder key amplifier transmits the key code, the Transponder Key ECU stops requesting the code and shuts off the power to the amplifier.

The example is for a 2007 Tundra. This does not work exactly the same for all models.

Transponder Signals


NOTE


Transponder Key ECU – Power & Ground

+B to GND: (J26 disconnected)• Always – 11V to 14V

IG to GND: (J26 disconnected)• Ignition OFF – below 1V• Ignition ON – 11V to 14V

GND to Body ground: (J26 disconnected)• Always – below 1Ω

Power & Ground

2007 Tundra

Several of the Transponder Key ECU’s terminals are for power and ground circuits. Diagnosis also involves testing at these terminals to be sure the ECU is receiving the proper voltage and has a good ground.

Power and Ground Circuits



Input

KSW to GND: (J26 disconnected)• No key in cylinder – 10KΩ or higher• Key In cylinder – below 1Ω

CTY to GND: (J26 connected)• Door closed – 10KΩ or higher• Door open – below 1Ω

Output

IND to GND: (J26 connected)• Immobilizer set (blinking) – alternates

between 11V to 14V and below 1V• Immobilizer unset (off) – below 1V

VC5 to GND: (J26 connected)• No key in cylinder – below 1V• Key In cylinder

• 4.6V to 5.4V until Transponder Key ECU receives key code (<0.5 sec.)

• Below 1V after key code received

Transponder Key ECU – Input & Output

2007 Tundra

An understanding of the system’s operation and inputs and outputs, makes diagnosis at the terminals easier.KSW. This ground-side switch closes when a key is inserted in the key cylinder. With no key in the cylinder, a continuity test between the terminal and ground would show an open circuit. With a key in the cylinder, the circuit would show continuity to ground and very low resistance.CTY. This ground-side switch opens and closes according to the driver door position. Resistance testing shows an open circuit when the door is closed, and a closed circuit when the door is open.IND. This terminal supplies power to the indicator light. It has battery voltage when the lamp is ON, and zero volts when the lamp is OFF. When the lamp is blinking, the voltage alternates.VC5. The TERMINALS OF ECU specifies that this terminal supplies nominal 5V power to the transponder key amplifier only when there is a key in the key cylinder. Power is only supplied until the Transponder Key ECU receives the key code, then it is switched off. This may take less than 0.5 second.

If the oscilloscope trigger is not set up properly, it’s possible to miss seeing the VC5 signal because the voltage switches on and off so quickly.

Inserting a key that has no transponder chip (or a faulty chip) forces VC5 to stay powered, providing adequate time for measuring voltage. Another option is to wrap the key-grip in foil to block its signal.

Terminal Values and Conditions

NOTE



VC5 to AGND: (J20 connected)• No key in cylinder – below 1V• Key In cylinder

• 4.6V to 5.4V until Transponder Key ECU receives key code (<0.5 sec.)

• Below 1V after key code received

CODE to AGND: (J20 connected)• No key in cylinder – below 1V• Key In cylinder – Waveform 1 (<0.5 sec.)

Transponder Key Amplifier

2007 Tundra

TXCT to AGND: (J20 connected)• No key in cylinder – below 1V• Key In cylinder – Waveform 2 (<0.5 sec.)

AGND to Body ground: (J20 connected)• Always – below 1Ω

While testing the Transponder Key ECU terminals, you would also test the CODE, TXCT, and AGND terminals at the J26 connector, if warranted.CODE. This is a communication signal sent to the Transponder Key ECUtransmitting the key’s ID code. The waveform shows a digital signal appearing as a momentary burst of data (less than 0.5 second) shortly after the key is inserted in the key cylinder.TXCT. This is the communication signal from the Transponder Key ECU to the transponder key amplifier. This waveform is also digital and appears as a momentary signal transmitted shortly after the key is inserted in the key cylinder.AGND. Because this is the ground circuit for the transponder key amplifier, it should show continuity to ground.

At the transponder key amplifier, the values for terminals VC5, CODE, TXCT, and AGND should be identical to those at the corresponding ECU terminals. By verifying the correct values are on the other ends of the wires, you eliminate the possibility of problems in the wire harness between the two components.

If the correct signal is verified on the CODE terminal of the Transponder Key ECU, it is not necessary to test the CODE terminal of the transponder key amplifier. Since the CODE signal is output by the amplifier, verifying the ECU is receiving it proves both that the signal is being output at the amplifier and the wiring between the two components is intact.

Transponder Key Amplifier Terminal

Values

NOTE

Terminal Values and Conditions (cont’d)



Engine Control Module

EFIO to GND: (J26 connected)• Ignition switch OFF – below 1V• Ignition switch ON – Waveform 3

2007 Tundra

EFII to GND: (J26 connected)• Always – Waveform 4

The TERMINALS OF ECU description indicates that EFII and EFIO are communication circuits. Therefore you expect to see digital data signals on these lines.Since EFII is the input signal from the ECM, a good signal at the Transponder KEY ECU verifies the ECM is transmitting and the wire to the ECM IMO terminal is intact.Similarly, a good signal at the IMI terminal of the ECM verifies the Transponder Key ECU is transmitting and the connection between the two is good.

ECM Terminal Values



Worksheet

Shop Worksheet:In this worksheet you will:• Use Techstream DATA LIST to make determinations related to the ID Code of the transponder chip embedded in the ignition key• Use a PicoScope to observe Immobilizer System waveforms under varying conditions and compare them to those in the Repair Manual.

Immobilizer


NOTES:



Power Distributor

Contact Relays• RDI Fan No.1 Relay• RDI Fan No.2 Relay• IGCT Relay • C/OPN Relay• A/F Relay

2006 Highlander HV

Power Distributor

Contact Relays Fuses

Semiconductor Relays

Front

Semiconductor Relays• Back-up Light Relay• Horn Relay• AC Water Pump Relay• Battery Fan Relay

• Head Light Relay LH• Head Light Relay LH• DRL No.2 Relay• DRL No.4 Relay• Rear Defogger Relay

Mode Monitor Terminal

In some vehicle models, a power distributor replaces the conventional relay box (engine room J/B). Whereas conventional relay boxes use contact-type mechanical relays, a power distributor replaces some of the mechanical relays with semiconductor relays. A semiconductor relay is a completely electronic circuit, reducing the size and weight of these components.

A feature of many power distributors is a protect mode. To protect semiconductor relay circuits in the event of overcurrent or overheating, the power distributor stops current flow through the circuit's semiconductor relay when an abnormality occurs. The power distributor soon restores current to the relay, but if the problem still exists, the power distributor again stops the semiconductor relay current flow. The power distributor continues this ON/OFF operation (protect operation) at a fast cycle until the problem is corrected.

Some models feature a mode monitor terminal on the power distributor. When the power distributor is operating normally, the voltage at the mode monitor terminal is approximately 6V. When the power distributor is operating in protect mode, the mode monitor terminal voltage is approximately 1V. Though this indicates protect mode is operating, it does not indicate which circuit is experiencing a problem.

Power Distributor

Protect Mode

Mode Monitor Terminal



Smart Junction Box (MICON)

MICON is short for “Microcomputer Controlled.”

MICON

These specialized electronic circuits can perform various functions such as converting electrical signals into multiplex data.They are typically located inside a relay block or junction block.

2005 Avalon

Junction boxes sometimes have programmable electronic circuits inside enabling them to carry out specific electronic tasks. These special circuits are represented inside junction boxes on electrical wiring diagrams with the label MICON (short for “microcomputer controlled” circuit).The specific function of any particular MICON is not described in the Repair Manual or EWD, and in fact is not important to diagnosis. Where measuring MICON signals is called for in a diagnostic procedure, the normal values are provided in the Repair Manual.

Smart Junction Box (MICON)



High Intensity Discharge (HID) Headlights

High-voltage arcing inside the metal halide bulb causes the metal atoms to emit light.

Headlight Unit

Time

Voltage Approx. 20,000V

Approx. 85VLight Control

ECU

Xenon GasLight

Light

Light

Bulb

Mercury Evaporation

Extremely high voltage starts the arc, then a lower voltage sustains it.

Light Control ECU

Headlight Relay

High Voltage Generation Circuit

High intensity discharge (HID) headlights produce a very bright light using an electric arc to excite atoms of xenon gas, mercury and metal halide. The light an HID headlight produces is very white and twice as bright as a comparable halogen bulb, but consumes almost half the power.Starting these lamps requires as much as 20,000 volts for the xenon gas to begin glowing. As the bulb warms up, the mercury evaporates and separates into mercury and halide atoms, creating an even brighter light. A light control ECU under each headlight provides:• High starting voltage necessary to ignite the lamp• Active control of current and voltage after startup to maintain optimum light output • A fail-safe function to stop headlamp operation in the event of an electrical fault or missing bulb.

High voltages in this circuit can damage test equipment and cause injury. Observe the safety precautions listed in the Repair Manual when servicing components in or near the HID headlight system.

The HID bulb and HID ECU service parts for 2004 – 2005 model year are NOT compatible with 2006 and later model year vehicles. Installing a 2004 or 2005 model year HID Bulb or HID ECU on a 2006 or later model year vehicle may cause an intermittent operation/flickering of the HID bulb.In most cases, when replacing the HID bulb, the HID ECU does NOT need to be replaced. In the event of HID ECU replacement, order the following part numbers: 81107-51050 (2004 – 2005 model year) or 81107-47150 (2006 –2008 model year). (Refer to T-SB-0030-08 for more information.)

High Intensity Discharge (HID)

Headlights

CAUTION


NOTE


Dynamic Laser Cruise Control

Operates in one of two modes:• Constant Speed Control Mode (same as conventional cruise control)

• Vehicle-to-Vehicle Distance Control Mode (uses the four controls shown below)

Constant Speed Control

No vehicle ahead

Decelerator Control

Accelerator Control

Follow-up Control

Closing in on vehicle ahead

Maintaining set distance from vehicle ahead

Resuming set speed

Set Distance

The Dynamic Laser Cruise Control has two operating modes.The constant speed control mode operates the same as conventional cruise control. The driver chooses a set speed and the cruise control works to maintain that speed.In the vehicle-to-vehicle distance control mode, Dynamic Laser Cruise Control employs a laser sensor to detect a slower-moving vehicle in the same lane and reduces the vehicle speed as necessary to maintain a fixed distance from the vehicle ahead. When the other vehicle is no longer in the path of travel, the cruise control accelerates to resume traveling at the set speed.

Dynamic Laser Cruise Control

Operation



Laser Sensor

The Laser Sensor CPU:• Uses data from the reflected laser beams to

calculate information on the vehicle ahead

• Does not react to stationary objects

Note: When installing, removing or changing the laser sensor, be sure to adjust the laser beam axis.

CPU

Laser Emitter

16°

Laser Receiver

4°

The laser sensor’s principle components are the laser emitter, laser receiver, and the CPU.• The laser emitter radiates laser beams forward.• The laser receiver receives the laser beams reflected by the vehicle ahead.• Based on the duration and input angle of the reflected beams, the CPU calculates the information on the vehicle ahead, and transmits this information to the Distance Control ECU. The CPU is designed so that it does not react to stationary objects.

Laser Sensor



Indicators and Error/Cancellation Codes

Constant Speed Control

Operating

Vehicle-to-Vehicle Distance Control

Ready

Operating (no vehicle ahead)

Operating (vehicle ahead)

Error/Cancellation Codes Any of the following cancels cruise control. Cruise control is prohibited until the conditions are remedied or the MAIN switch is turned on again.

• Malfunction in the laser sensor or control system

• Laser sensor dirty

• Adverse environmental condition (weather, sunlight)Distance Setting

Long Middle Short

The driver is able to set the following parameters and sees the related indicators on the display:Mode – Constant speed control mode or vehicle-to-vehicle distance control mode.Distance – Long, middle, or short. (The actual distance represented by each setting is based on vehicle speed. At 55 mph, the distances would be approximately 245 ft., 165 ft., and 100 ft.) Set Speed – Above approximately 25 mph. (In vehicle-to-vehicle distance control mode, the set speed cannot exceed approximately 85 mph.)

Certain conditions will cancel cruise control operation and display a code on the cruise control indicator.The C1 code is set when the laser sensor is dirty.The C2 code is set when:• The wipers operate at HI or LO speed (including AUTO mode).• The laser sensor receives a strong light from the front of the vehicle, such as sunlight.• The measurement becomes extremely unstable due to poor weather conditions.The following conditions set the E3 code:• Malfunction in the laser sensor• Displacement of the axis of the laser sensor• Other malfunction in the dynamic radar cruise control system

Indicators

Error/Cancellation Codes



Constant Speed Control • The Distance Control ECU signals the ECM to maintain the

set vehicle speed.

• The ECM compares actual speed with the set speed and regulates the throttle to maintain the set speed.

Laser Sensor

Distance ControlECU

Vehicle Speed Signal

(SPD)

Cruise Control Switch


Throttle Control Motor

ECMCAN

While no vehicle is detected in the path ahead, the system operates similarly to conventional cruise control.

NOTES:



Decelerator Control • A deceleration request is sent to the ECM. The ECM closes the throttle valve.• If further deceleration is needed, a brake request is sent to the ECM. The ECM

sends a brake request to the Skid Control ECU.• If deceleration is not adequate, the VSC warning buzzer sounds to alert the driver

to apply brakes.

Laser Sensor

Distance ControlECU


(SPD)


ECM

Brake Actuator• Skid Control ECU

Stop Light Control Relay

VSC Warning Buzzer

Stop Light

CAN


Decelerator control occurs when a slower moving vehicle is detected in the path ahead.

NOTES:



Follow-Up Control • With the distance control switch, the driver selects between long,

middle, and short following distance. • When the set distance is achieved, the ECM regulates the throttle

to maintain the set distance between vehicles.

Long

Middle

Short

Note: The actual following distance varies depending on vehicle speed.

Set Distance

Laser Sensor

Distance ControlECU


(SPD)

Distance Control Switch

ECM Throttle Control Motor

CAN


Follow-up control maintains the set distance between the vehicles.

NOTES:



Accelerator Control • When there is no longer a vehicle ahead, an

acceleration request is sent to the ECM. • The ECM regulates the throttle to reach and maintain

the set speed.

Laser Sensor

Distance ControlECU


(SPD)

ECMCAN



Accelerator control resumes the set speed when the slower moving vehicle is no longer in the path ahead.

NOTES:



System Diagram

2005 Avalon

Laser Sensor Distance ControlECU

ECM

CAN

GatewayECU

• Combination Meter (SPD)

• Stop Light Switch• Cruise Control Switch• Accelerator Pedal Position Sensor

• Throttle Position Sensor

• Park/Neutral Position Switch

Steering Angle Sensor

Brake Actuator• Skid Control ECU

Yaw Rate & Decelerator Sensor

DLC3

Distance Control Switch VSC Warning Buzzer

Stop Light Control Relay

Stop Light


Automatic Transmission • Shift Solenoid Valves

BEAN

Combination Meter• Cruise MAIN Indicator Light• Master Warning Light• Constant Speed Indicator

Light• LCD• Buzzer

Combination Switch• Wiper Control Switch• Taillight Control Switch

Rain Sensor

For signal flow, locate the Transmit/Receive Chart in the Repair Manual.

Communication between the laser sensor and the Distance Control ECU is serial data, although it is not part of the vehicle’s standard multiplex networks.

NOTES:



Distance Control ECU Waveforms

• LRDD – GND• Ignition ON

• LRRD – GND• Ignition ON

2005 Avalon

These are waveforms for the serial data flowing between the laser sensor and the Distance Control ECU.

NOTES:



Laser Radar Sensor Waveforms

• LRDD – SGND• Ignition ON

• LRRD – SGND• Ignition ON

2005 Avalon

These are the same serial data signals as before, except now measured at the laser sensor and viewed at different voltage and time scales.

NOTES:






CAN Waveforms• Normal CAN Signal• Short Circuits• Open CircuitsBEAN Waveforms• Normal Bean Signal• Short to Ground• Dual Trace• Open Circuit

Appendix

AAppendix

Transistors• Bipolar Transistor• NPN and PNP Transistors• How a Transistor Works• Transistor Switches• Transistor Amplifiers• Digital Circuits• Analog to Digital Converter• Logic Gates

Return to Simple ECU Outputs<<<<



Bipolar Transistor

A bipolar transistor is a solid-state electronic device.

Base

Emitter Collector

Base

Emitter

Collector

• Used in electronic circuits as an electronic switch, to amplify weak signals, and for converting signals between analog and digital.

• Also used to construct logic gates which are essential components of microprocessors.


The invention of the transistor in the late 1940’s launched the electronics age. Transistors replaced vacuum tubes in radios, amplifiers and many other electrical devices, offering faster operation, lower power consumption, and lower cost in a compact form.The transistor turned out to be a very versatile invention that could be used for:• Switching devices• Current regulators• Amplifiers• Logic circuits• Analog-to-digital (A-to-D) signal convertersIn the late 1950’s, the invention of the integrated circuit enabled transistors and other electronic components to be miniaturized and mass produced. In the 1960’s, it was these miniature, low-cost integrated circuits that made complex electronics possible and ushered in the computer age.Today, transistors are still available as discrete components with three wires sticking out of them for use in simple electronics. The near-microscopic transistors in modern computer chips, however, are far more numerous with a typical chip containing over 200 million transistors.

Transistors



NPN and PNP Transistors Transistors are manufactured from silicon – an insulator.

• The silicon is “doped” with a small amount of impurities to create material having a few extra electrons (n-type) or a small deficiency of electrons (p-type).

• The different types are sandwiched together to create a transistor.

P-N-P transistor

N-P-N transistor

Base

Emitter

Collector

Base

Emitter

Collector

Emitter

Collector

Base

N-type

N-type

P-type

P-type

P-type

N-type

Emitter

Collector

Base

Construction Symbol

Base

Emitter

Collector

Base

Emitter

Collector

Diode Representation


A bipolar junction transistor (BJT) is either a NPN or PNP type. Both work similarly.Although the bipolar junction transistor was the first to be mass produced, it has one undesirable characteristic. Its low input impedance between the base and emitter makes it difficult to match impedances in multi-stage amplifiers. Most modern transistors are field-effect transistors (FETs). Although field effect transistors work somewhat differently, they accomplish the same functions that bipolar transistors do, but offer high input impedance. Various types of FETs include junction (JFET), insulated gate (IGFET) and metal-oxide-semiconductor (MOSFET).

Transistor Types



How a Transistor Works

When current is appliedThe few extra electrons in the N-type material migrate to the P-type layer creating an electrically neutral region called the depletion layer. This layer acts like an insulator.

No current flow

Applying sufficient voltage to the base overcomes the depletion layer enabling current to begin flowing.

Depletion layer N

N

P

Depletion layer

N

N

P

Emitter GND

Collector +12V

Base +5V

+12V

GND

Current flow

Even with voltage applied to the collector, current cannot flow.


In an NPN transistor, the voltage at the collector must be higher than the voltage at the base, and the voltage at the base must be higher than the voltage at the emitter. NOTES:



Transistor Switches

A transistor can be used to switch another circuit in the same way as a relay, allowing a small current to control a circuit with much greater current flow.

12V 12V

5V

5V


A common transistor application is as a switch.NOTES:



Transistor Amplifiers

Keys to Operation

12V

Weak input signal voltage

Amplified output signal voltage (phase shifted)

• Voltage at the base regulates current flow through the transistor.

• A minimum voltage at the base is required to start current flow.

• Increasing the voltage at the base lowers transistor resistance and increases current flow through the collector-emitter.

NPN Bipolar Transistor Amplifier Circuit

Rb

Rc

Input Line

Without Rc, voltage on the output line would always be 12v.

Transistor resistance varies with voltage applied to the base. Return to Simple

ECU Outputs<<<<

Within a specified range, varying the current flow at the base varies the current flow through the transistor. This allows the transistor to be used as an amplifier.NOTES:



Digital Circuits

Digital circuits require only two values – ON and OFF.

Examples:

In a BEAN circuit, 0V = OFF and 10V = ON

In a CANH circuit, 2.5V = OFF and 3.5V = ON

In a CANL circuit, 2.5V = OFF and 1.5V = ON

In many discussions of digital communication, the actual voltages used for ON and OFF in different networks is not important.

Therefore, 0 and 1 are used to represent the OFF and ON voltages.

Time

Voltage

0 1 0 0 01


In a digital circuit, a transistor is ON when the proper voltage is applied to the base. Otherwise, the transistor is OFF.NOTES:



Analog to Digital Converter

The transistor turns ON when the threshold voltage reaches 5V and turns off when the voltage drops below 5V, converting the analogsignal into a digital signal.

B+

Alternating (analog) voltage signal input

Transistor threshold voltage (5V)

Digital signal outputReturn to Simple ECU Outputs<<<<

An NPN transistor requires a minimum voltage applied at the base in order for current to flow. Called the threshold voltage, it turns the transistor ON.This property allows a transistor to convert analog signals at any particular frequency into digital signals with the same frequency, by outputting a digital pulse each time the analog wave reaches its peak. This type of circuit is called an analog-to-digital converter, or an A-to-D converter.

There are cases in which you may be troubleshooting an A-to-D converter circuit and find you have an analog input signal but no digital output. In this situation, verify that the peak voltage of the analog wave is sufficient to reach the transistor’s threshold voltage.

Analog to Digital Converter

NOTE



Logic Gates Transistors are used to build logic gates. Logic gates are essential to how microprocessors function. A logic gate is an electronic circuit that outputs either an ON or OFF signal depending on:

• The input values to the circuit

• The circuit’s logic rules

NOT

NAND NOR

AND OR XOR

XNOR

Logic Gate Symbols

Logic Gate Truth Table

A B AND NAND OR NOR XOR XNOR0 0 0 1 0 1 0 10 1 0 1 1 0 1 01 0 0 1 1 0 1 01 1 1 0 1 0 0 1

INPUTS OUTPUTS


One of a computer’s remarkable capabilities is in its seeming ability to make “decisions.” In reality, however, a computer can only evaluate situations it is programmed to recognize. At the most fundamental level, that programming is accomplished using logic circuits.Logic circuits use transistor-controlled logic gates to convert specific combinations of inputs into predetermined outputs. As an example, consider the simple logic of the automatic light control system:

IFLight control switch is in the AUTO position, andLight control sensor detects LOW ambient light, andIgnition switch is ON

THEN Turn headlights ONTurn taillights ON

To make this circuit operate, we need a logic circuit that has three inputs and two outputs. When all three inputs are ON, then both outputs should be turned ON.To build this type of circuit, we would need a specific combination of logic gates. It takes an average of 17 transistors to build a single logic gate.

Logic Gates



Normal CAN Signal

CANL CANH

<<<<Return

The characteristics of a normal CAN signal are:• CANH and CANL idle at 2.5V.• Data signals appear in periodic bursts.• CANH signal ranges between 2.5V and 3.5V.• CANL signal ranges between 2.5V and 1.5V.• The CANH and CANL signals are mirror images of each other.

Normal CAN Signal



Short CANH to CANL

CANL CANH

<<<<Return

Shorts and opens in CAN communication circuits tend to produce signature waveforms. Understanding circuit behavior during certain types of malfunctions and being able to identify the waveforms they create makes CAN diagnosis easier.

When CANH and CANL are shorted together, it is impossible to generate a differential voltage on the two lines. The matching high and low voltage pulses sent by the ECUs cancel each other because the lines are connected.This condition is indicated by a flat line at 2.5 volts.

CAN Shorts and Opens

Short CANH to CANL



CAN Short to B+

Short CANH to B+

Short CANL to B+

CANL

CANL

CANH

CANH

<<<<Return

Shorting CANH to B+ boosts the circuit’s idling voltage from 2.5V to battery voltage. Though the ECUs in the circuit are unable to raise CANH voltage above B+, they are able to lower CANL enough to create a voltage differential and the appearance of communication. The apparent signal on the CAN bus may be enough to cause one or more ECUs to show up in a CAN bus check. Despite that, communication on the circuit is still not reliable.Detecting this condition does not require an oscilloscope. If you were to test CANH and CANL with a DVOM, CANH average voltage would be approximately B+, while CANL average voltage would be between 6V and 10V.

When CANL is connected to B+, the circuit’s idling voltage becomes battery voltage. The ECUs cannot drag the CANL line voltage lower because it is connected directly to B+, nor can they raise the CANH line voltage above B+. The voltage spikes on the line are not interpreted as communication and none of the ECUs appear in the CAN bus check.Measuring CANH and CANL with a DVOM would likely show both lines very close to B+.

Short CANH to B+

Short CANL to B+



CAN Short to Ground

Short CANH to Ground

Short CANL to Ground CANL

CANL

CANH

CANH

<<<<Return

Grounding the CANH side of the CAN bus brings the idling voltage of both lines to 0V. With CANH tied to ground, the ECUs cannot generate a positive voltage on the line. On the CANL line, the ECUs can’t create a pulse lower than 0V. The spikes on the line are not interpreted as communication and none of the ECUs appear in a CAN bus check.Measuring with a DVOM would show an average 0V on each line, indicating the circuit is grounded.

When CANL is grounded, the ECUs are still able to generate a differential voltage on CANH. These signals may be interpreted as communication and one or more ECUs can appear in the CAN bus check even though communication is not reliable.In this case, measuring with a DVOM would show ground voltage on CANL, and a slightly positive voltage on CANH.

When a connection to B+ brings CANH high, or when a connection to ground brings CANL low, there is still the appearance of communication on the circuit. In the first case, CANL can still be brought low to create a voltage differential, and in the second case, CANH can still be brought high. Though communication on the circuit is compromised, ECUs may still appear in the CAN bus check in either case.On the other hand, bringing CANH low by grounding it, or bringing CANL high with a short to B+ renders the circuit incapable of generating any kind of voltage differential. These are the cases when the ECUs do not show up in the CAN bus check.



NOTE



Open in CANH or CANL (Main Bus)

Open in CANH

Open in CANL CANL

CANL

CANH

CANH

<<<<Return

With an open in either CANH or CANL on the main bus, part of the circuit looses its connection with one of the terminating resistors. The purpose of the resistors are to help keep signals from “bouncing” and generating noise.Though these waveforms show apparent communication, you can tell the circuits have a problem because:• Idling voltage is NOT 2.5V.• CANH voltage range is NOT 2.5V to 3V.• CANL voltage range is NOT 2.5V to 1.5V.

Open in CANH or CANL (Main Bus)



Open in CANH and CANL (Main Bus)

CANL CANH

<<<<Return

With opens in both CANH and CANL on the main bus, the circuit is divided into two parts, each having only one terminating resistor. As in the previous example, this introduces noise into the circuit. Also, because the two halves of the network are separated, the communication signals occurring on one half are different from those occurring on the other half. Comparing the CANH signals (or CANL signals) on each half would show them to be different from each other. This can be exploited in diagnosis by systematically moving one probe toward the other in the circuit and comparing waveforms. When the waveforms become identical, the probes are now on the same half of the network, and the open is between the current and previous test points.

Open in CANH and CANL (Main Bus)



Normal BEAN Signal

The characteristics of a normal BEAN signal are:• Signal idles at 0V.• Data signals appear in periodic bursts.• Signal peak is 10 to 12V.

BEAN Signals



BEAN Short to Ground

When the BEAN communication bus is shorted to ground, the ECUs are unable to raise the line voltage to send signals. The line voltage is flat-lined at 0V.A diagnostic process for locating a short to ground is to view the BEAN waveform with an oscilloscope while disconnecting parts of the network. When the short to ground is removed from the network, normal communication resumes. For example, if communication returns when half the circuit is disconnected, the location of the short to ground is in the part of the network that was disconnected. Continue isolating sections of the network until you find the exact location of the short to ground.

BEAN Short to Ground



Normal BEAN, Dual Trace

Probes are placed at two different points on a normal BEAN communication line to illustrate that the signals are identical at all points in the network.

Probes are placed at two different points on a normal BEAN communication line to illustrate that the signals are identical at all points in the network.

NOTES:



BEAN Open Circuit, Dual Trace

If the BEAN network is divided by one or more opens, the signals in the isolated networks are no longer identical.

If the BEAN network is divided by one or more opens, the signals in the isolated networks are no longer identical.

NOTES:





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673 Electronic and Computer Controlled Systems Technician Handbook 06-22-09